# DIY Belt Grinder Build Questions



## devils4ever (Feb 8, 2021)

I'm thinking about building a 2X72 belt grinder for shaping/sharpening HSS lathe tooling and general shaping/deburring metal parts. I have a 6" bench grinder now and it works, but it's slow. But, I have some questions on the design and construction.

Why are most belt grinders 3 or 4 wheels? I'm thinking 2 vertical wheels would be simpler to build and easier to keep the belt tracking. It would also take up less bench space.
Is variable speed really needed? Why would you not keep the speed maxed out at all times?
Can this be made from aluminum instead of steel? Aluminum is lighter, corrosion resistant, and easier to machine.
A lot of designs allow the belt to be placed horizontally. When would this be useful?
I see a lot of designs that allow the belt to be tilted as well as the rest. Why do you need both to tilt? Isn't one tilting enough?
I understand a glass platen is better than steel. Is it because it is flatter and more wear resistant? 
I would probably buy the wheels as a set since it would push my mini-lathe to the limit. What are good diameters for the drive wheel?
What SFM is desirable on the belt?
If I do go with variable speed, I'm guessing a 3-phase motor and VFD are the way to go?
I know mikey recommends ceramic belts. Looking at MSC, they go from 36 grit to 220. Is 220 fine enough for lathe bits? What is the equivalent grinding wheel grit?
That's all for now! Thanks all!


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## projectnut (Feb 8, 2021)

Thake a look at the Burr King grinders.  They are essentially the Cadillac of belt grinders.  They are the best built longest lasting machines of this type I am aware of.  They have dozens of different models and belt sizes.  The type of work you want it for generally dictates the size and style you want.  Each machine has a short description as to it's features.



			Belt Grinders


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## Daffy (Feb 8, 2021)

I've built a couple 2x72's out of treadmills that work really well. takes some patience to get everything aligned for tracking is all. Longboard skateboard wheels are excellent idler wheels. Last one I built has less than $35 in cost in it withholding my time and runs like a screaming demon. If $$ wasn't an object I'd buy a Bader but I digress, I'm a cheepo where I can be. 

2 wheel setup can be done, going to sit pretty high, Grizzly uses this design.
Variable speed isn't a necessity, but very useful for finer grit belts to keep the heat transfer minimized.
Aluminum? Wheels for sure, suppose the rest could be made out of it too.
Horizontal, mine aren't, again suppose it would be useful just so far haven't had the need for it.
Glass platen, less belt wear on the back, cooler running, nice and flat.
Drive wheel size determined by rpm of your drive source, mine runs at ~4500 rpm max, faster than it needs to.
SFM?, guess I never got that technical about it.
Variable speed motor source, I'll take the DC motor anytime.
I make knives and sharpen them. My belts go from 36 to 2500.

Hope that helps.


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## jwmelvin (Feb 8, 2021)

I’m very slowly working on one. My design:

targeting 7k FPM as the max surface speed; and

using TEFC 3-phase motor to avoid issues with ferrous grinding dust and a permanent-magnet motor. 

I think the configuration for tilting axes (belt, work support, platen) is mostly about convenience for whatever shape work you happen to be working on.


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## Masterjuggler (Feb 8, 2021)

I also built my own and here are some of my own opinions:

1) A large space in the middle allows for more attachments than just the flat platen, like a large and small contact wheels, or even a surface grinder attachment on the bottom. I also have mine on a bench rather than free standing, so it lowers the overall height.
2) YES. I use slow speeds all the time for delicate work. Even if the motor itself isn't variable speed, just using a step pulley like on a drill press is enough.
3) People have made them out of aluminum. There are even some plywood designs. Steel is usually just the cheapest and easiest to weld in any shape.
4) I've never really desired it myself, but it helps with burrs. When you grind perpendicular to a face, you can get a massive burr on the bottom. IT also gives you a larger strip of the flat platen to work with.
6) Generally wear resistance. I'm using a piece of ceramic glass for mine, though the static buildup can be pretty insane if you don't hold a finger to the metal frame. There are countermeasures for this though, just like with dust collector static buildup.
7) Like Daffy said, 2" wide longboard wheels work well, they're what I'm using right now. You could also just glue some MDF sheets together and turn them on your mini lathe. My main drive wheel is MDF laminate.
9) I'm using a 3ph motor I got for about $30. If you're doing this on the cheap, just scan ebay for used ones, they're not uncommon. If you have a single phase motor available to you, just make some stepped pulleys out of plywood. I like to have pulleys with my 3ph motor because it gives me torque options.
10) Very opinionated, but I wouldn't go over 60 or 120 grit with ceramic. Over that just isn't cost effective. You'll get a lot of use out of the 36 and 60 grits though. If you're grinding HSS lathe tools, 220 is fine before a quick stoning.


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## devils4ever (Feb 8, 2021)

I forgot to mention that I don't have a welder. So, my design has to be bolted together!

I do like the design that Phil Vandelay uses on YT except his is metric and I would have to convert it. See it here.


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## Daffy (Feb 8, 2021)

Really nice design here.


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## mikey (Feb 8, 2021)

devils4ever said:


> I'm thinking about building a 2X72 belt grinder for shaping/sharpening HSS lathe tooling and general shaping/deburring metal parts. I have a 6" bench grinder now and it works, but it's slow. But, I have some questions on the design and construction.
> 
> Why are most belt grinders 3 or 4 wheels? I'm thinking 2 vertical wheels would be simpler to build and easier to keep the belt tracking. It would also take up less bench space.
> Is variable speed really needed? Why would you not keep the speed maxed out at all times?
> ...



1. You actually do not need to go with a 2X72. There are a lot of other common belt sizes and a 42 or 48" belt would do fine while allowing you to use two wheels instead of four. The 72 belt is commonly used by knifemakers and are readily available. Each wheel has a job - drive, tracking and on a platen, two wheels support the belt as it runs over a platen. Contact wheels have an obvious function.
2. VS is nice to have when using fine grit belts. High speeds tends to eat up the abrasive quickly and also causes the splice to thump annoyingly under the work.
3. You can go with aluminum; others have. The thing to consider is the modulus of elasticity of aluminum is 1/3 that of steel so for parts that are under tension, steel is a better option. The chassis, if properly braced, can be aluminum.
4. Horizontal positioning is useful for grinding wood, knife handles, edges and so on. Not necessary but nice if you can design it in.
5. Tilt is good for grinding bevels while keeping the tool rest flat. Think beveling the edges of square tubing before welding.
6. Yes. A ceramic glass platen will remain flat for years in a hobby shop. When grinding tools, a flat platen is critical to controlling your geometry. Of all the mods you can do to a belt sander, I consider a glass platen to be #1.
7. 5-6" is common.
8. For metal grinding, supposedly somewhere near 6K or more is desirable. I have gotten along fine with much slower belt speeds but if you have a VS motor that can hit those speeds then you'll be grinding, not sanding.
9. VFD's are commonly used on these belt sanders. However, if you are going to be doing a lot of detail work at slower speeds then a DC motor might be a good option because you will retain torque at lower speeds.
10. For shaping, a 36 grit ceramic belt is really good, while 80-120 is good for smoothing out the coarse grind marks. You can step up through the grits to put a near mirror finish on a lathe tool if you desire. I would look at the Red Label ceramic belts on Amazon if I were you.


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## devils4ever (Feb 9, 2021)

Ok, so looking at the motor, I'm thinking a 3-phase, 1-1/2 HP, totally enclosed fan cooled unit such as this would work? It is 3,470 RPMs. If I calculate this correctly for a 6 inch drive wheel, the max SFM is RPM X (drive wheel diameter in inches X PI) * (1 ft/12in) = 3470 X (6 X 3.14) / 12 = 5,448 SFM. To hit above 6K, I would need a 7 in drive wheel.

I'm not sure on VFDs since I've never used one. I'll have to look at those units as well.

I'm thinking of staying with the 4 wheel design and using steel for the parts.


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## jwmelvin (Feb 9, 2021)

With a VFD you can drive the motor past it’s rated speed. Increased speed would mean increased power of torque is constant, so I believe typically it would run with constant power (decreasing torque as speed exceeds rated speed). I am not sure what the practical limits are but I went with a 6” drive wheel and 3600 rpm, 2hp motor.


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## Masterjuggler (Feb 9, 2021)

3,470 rpm is fine, and you can always change the size of the drive wheel (assuming you're direct driving). I use a 2hp 1725 motor with about a 3.5 inch drive wheel, normally on a 5:4 pulley ratio from the motor, and I'm pretty happy with the speed and torque. I guess that would translate to roughly 2000 SFM. That's the middle of my pulley range though, so I could go higher or lower. I still suggest you use some pulleys so you can change it around and get a high torque low speed setup if you want.

Also if you're going to have a very fast setup, I would recommend you not get longboard wheels with cheap 608 bearings. They'd just explode on you with that kind of demand. Use at least 1/2" ID bearings, and either buy or turn your own wheels. Like I said, laminated MDF is a good choice, especially if you're not doing production work.

If you're not in a rush, watch ebay or FB marketplace for motors. You'll see some amazing deals on them pretty regularly, even ones that ship out. No need to pay full price for a new motor, especially if you're looking to save money overall.

One thing to keep in mind is that for low grit ceramic belts, you want enough torque that you can really shove work into the belt. At least on most ceramic belts I know of, the grit is able to fracture and reveal new cutting edges. You could also use a bench grinder wheel dresser for that.


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## devils4ever (Feb 10, 2021)

I was hoping to go with direct drive to make things simpler.

So, is 2 HP needed or is 1-1/2 HP enough?


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## rwm (Feb 10, 2021)

Direct drive with 3400 rpm and a 6" wheel is a good target. 1.5 HP is overkill in my opinion; I used 3/4 and it is fine. The bearings you select are critical at these speeds. Make sure they are properly rated. I had to change mine out and redesign the pulley to fit. I built my 2 x 48 out of aluminum with the vertical support made of steel. That worked out well. Here is the thread if it give you any ideas.









						2 X 48 Belt Grinder (again)
					

I started on my belt grinder! I built this motor from scratch from scrap bin parts. I think it looks OK, although the capacitors are a little big.  (Yes I know it reminds you of your ex but please refrain from commenting.)      Specs are 3/4 HP @ 3450 RPM. Already blows 15 amp circuits. It's a...




					www.hobby-machinist.com
				




Robert


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## Masterjuggler (Feb 10, 2021)

The motor size depends how you plan to use it. I like to really lean into it, and my 2hp 1725 rpm motor is about right for me. If I put my body weight into it I can get it to stall on large pieces. 

Like I was saying before, you need the pressure to break the grit on ceramic belts to expose new edges, and you won't get a ton or torque out of a 3400 rpm motor with a 6" drive wheel. With a given motor horsepower rating, if you double the speed, you halve the torque. Power = speed x torque

I recommend you include a pulley system so you can get a higher torque setup if you want, assuming you go with a high speed motor.


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## rwm (Feb 10, 2021)

I can stall my grinder, but if I do, the workpiece and the belt are definitely overheated. I am running Zirconia belts and I have had them come apart from overheating.
R


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## devils4ever (Feb 11, 2021)

I found this Dayton motor at Grainger that is 2 HP, 3 phase, 3480 RPMs, 56C frame, and TEFC for around $270. So, I'm thinking of using that. I see one Youtuber uses an Ironhorse motor and is highly recommended and is only $169, but it's out of stock. The Grainger motor I can pick up locally without shipping fees.

For the VFD controller, I'm thinking of using this which is under $100. 

I may have to buy the drive wheel since my 7X16 mini-lathe would have a tough (impossible) time turning a 6" diameter. I may wind up buying a set although most sets seems to use a 4" or 5" drive wheel.

I'm still searching for power and drivetrain options. I need to research the glass platen, too.


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## rwm (Feb 11, 2021)

For a 2HP motor I would want to know the amp draw for the VFD. Do you have 20 amp circuits or 240V available?
2HP on a 120v 15 amp circuit at the 80% rule is gonna be close.
Robert


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## devils4ever (Feb 11, 2021)

Yes, I have 220V, 20A power available.


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## Masterjuggler (Feb 11, 2021)

I still think you should be looking toward used motors instead of trying to get one new. Even if they bearings need to be replaced, they're going to be far more cost effective than getting something from grainger, which I've always found to be super expensive anyway. Here are two new options I found, but you can even get them cheaper used if you wait and keep looking. I gotten similar motors for about $40 shipped on multiple occasions.








						Weg Electric Motor Model GM2000-KUTF-14, 1740 RPM 2 HP 3PH 208-230/460V 60HZ  | eBay
					

WEG ELECTRIC MOTOR FOR 2HP 208-230/460V 60HZ. SEE LABEL PICS FOR ALL INFO.



					www.ebay.com
				











						New Marathon AC Motor 1725 RPM 1.5HP 3PH 208-230/460V  | eBay
					

Checkerboard Farms-. Continuous Duty.



					www.ebay.com
				




I like that VFD you linked and use two of them myself, though they are going to be less reliable than a more expensive name brand in the end. The nice thing about that specific one compared to other chinesium VFDs is it has a heatsink fan that only runs when the machine runs.


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## devils4ever (Feb 11, 2021)

I was looking at 3400+ RPM motors to get the belt speed up. Both of those you listed are around 1700 RPMs.


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## projectnut (Feb 11, 2021)

Before you get too carried away specing out components you might want to check eBay for already built professional models.  I've seen several KAR-RY models ranging in price from $150.00 to about $650.00.  Most of them are along the east coast.  There are also a few in Ohio.  At these prices it might be less expensive (even with shipping) to buy  an existing one rather than spend close to $1,000.00 in parts and time to build one.

Here are links to a few available.









						kar-ry belt grinder  | eBay
					

Find many great new & used options and get the best deals for kar-ry belt grinder at the best online prices at eBay! Free shipping for many products!



					www.ebay.com
				












						Kalamazoo 2" X 48" Belt Sander LOCAL PICK UP ONLY.!!!!!  | eBay
					

Find many great new & used options and get the best deals for Kalamazoo 2" X 48" Belt Sander LOCAL PICK UP ONLY.!!!!! at the best online prices at eBay! Free shipping for many products!



					www.ebay.com
				












						KAR-RY Belt Sander Grinder   | eBay
					

For Sale (1) Used KAR-RY Belt Sander / Grinder. Belt size - 1" x 42". Loading is availab le. Machine net weight approx 330 lbs. Single Phase 110v Electrics.



					www.ebay.com


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## devils4ever (Feb 11, 2021)

Yeah, but where's the fun in that!


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## projectnut (Feb 11, 2021)

devils4ever said:


> Yeah, but where's the fun in that!


You must have more time in the shop than I do.  Even though I've been "retired  15+ years I still don't get as much time there as I'd like to.  I must admit though I've gotten more time in the last 10 months than I have in the previous 10 years.  This last month has been a windfall as far as shop time.  It's barely gotten above 0* the last couple weeks, and the lows have been in the double digits below 0*.  

Even the dogs don't want to spend much time outdoors.  Normally they would like to go for walks and be outside several hours throughout the day.  The last couple weeks it's been a pain to get them out for a single lap around the yard.  Once their deeds are done it's a quick sprint back to the house.

Too bad those machines are so far away from me.  I like them and would be all over them if they were within a couple hours drive.


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## devils4ever (Feb 11, 2021)

Unfortunately, with COVID I've got lots of time. I'm looking for projects. 

With the cold, snowy weather of late, I can't even enjoy going outside.


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## devils4ever (Feb 12, 2021)

I notice some of the belt grinder wheel sets on ebay come with 2 crowned wheels, the drive wheel and the track wheel. I always though only one of the wheels should be crowned to prevent the belt trying to follow 2 crowned wheels that might be out of alignment somewhat.

 Is this true?


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## ttabbal (Feb 12, 2021)

I'm using one of the plastic sets from ebay. They work great and I've never had a problem with the 2 crowned wheels. If it ends up causing a problem, you could always toss one in a lathe and flatten it out.


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## devils4ever (Feb 16, 2021)

I found this VFD drive on eBay for only $63 which is the same as the one on Amazon for $97.


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## Masterjuggler (Feb 16, 2021)

With the cheap chinese VFDs, the rated power is usually on the optimistic side. I had one burn out when I sized it exactly to the motor. 1.5KW = 2HP, I'd get the 2.2KW VFD if you go with that motor.

Brand name VFDs are another matter of course, their ratings are much closer to reality.


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## devils4ever (Feb 16, 2021)

Thanks. You're right. I didn't notice the lower HP rating. I guess that's why it's cheaper.


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## devils4ever (Feb 20, 2021)

Ok, I'm leaning towards a KB Electronics VFD Drive now. It's UL listed and sealed which is very attractive. I know it's more than 3X the price, but I'm using the "buy once, cry once" motto.

So, I think the KBAC -27D, KBAC-29, or KBAC-29 (1P) would work for a 2 HP motor. Sound correct?


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## ttabbal (Feb 20, 2021)

I only hear good things about the KB VFDs. If you have the budget, you can't go wrong with them. I'm using a cheap one, but I do have to keep it well clear of the dust.


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## devils4ever (Feb 22, 2021)

I got my motor, VFD, and wheels ordered. I'm still designing this in FreeCAD, but it's close to completion.

For reference:
Motor: Dayton 36VF69 from Grainger. (Detail: 2 HP, 3-phase, 3480 RPMs, 56C frame, TEFC, Inverter rated, UL, ball bearings, 5/8" shaft)
VFD: KBAC-29 (1P) 10001, rated to 3 HP at 220VAC 1 phase input
Wheels: Belt Grinder 2x72 Wheel Set knife Grinder 6" Drive 5/8" Bore 4" Track 2" Idler from grinder-pro on eBay

I'm trying to determine how much force is needed on the tracking wheel. Is it 10 lb, 20 lb, 30 lb, 40 lb, or more? I plan on using a gas spring unless that are better alternatives.


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## ttabbal (Feb 22, 2021)

The design that uses nested tubes and a wire spring calls for 30lb. I would guess a similar amount of force would be good for a gas spring using the lever arm design.


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## devils4ever (Feb 22, 2021)

ttabbal said:


> The design that uses nested tubes and a wire spring calls for 30lb. I would guess a similar amount of force would be good for a gas spring using the lever arm design.



Nested tubes? Could you elaborate?


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## rwm (Feb 22, 2021)

Mine probably has about 10lb force on the arm. I just used a regular spring. See what other answers you get.
Robert

Edit: should clarify. My pulley probably has about 10 lbs of force. The spring is under more tension because of the geometry.
R


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## Masterjuggler (Feb 22, 2021)

What are you using for a spring? I've got an 85lb air spring that I can pin to different positions on the arm, I usually keep it at about 40lb vertically at the wheel, but it depends what I'm doing. I go down to roughly 15lb for flexible belts to get into curves, and around 60lb for heavy belts.


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## ttabbal (Feb 22, 2021)

devils4ever said:


> Nested tubes? Could you elaborate?



The common "simple" design. Rather than the pivot arm like the photo @Masterjuggler posted, it's like a trailer hitch with a vertical post that the post holding the tracking wheel fits into, with a coil spring at the bottom. It works, but there is a bit of wobble in the post due to the fit between the square tubes. When I take the time to work on mine, I intend to move to a pivot setup as it does mess with the belt tracking a little. I use a wedge in there to keep it from moving about right now. I like the one @Masterjuggler did with different mounting points. That is a nice idea to adjust for various needs while still being a pretty simple to build design. 









						BG-272 DIY 2 x 72" Belt Grinder
					

DIY 2" x 72" Belt Grinder Project   Like almost every newbie knifemaker owning a decent belt grinder is dream. When I realized the price of...




					dcknives.blogspot.com


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## devils4ever (Feb 22, 2021)

Okay, I think I got it. Thanks.

I'm assuming a gas spring offers dampening of the motion. Is that correct? A simple spring is a lot cheaper!


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## Masterjuggler (Feb 22, 2021)

The one I did is EXCEEDINGLY jank lol. It's thin wall tubing welded together with some microwave transformers with rewound secondary coils, which is why it looks like bird poo and has holes blown through it. To keep the arm from wobbling, I cut some washers out of a soda bottle. I had intended to weld a proper handle to the arm, but was too excited to use it and instead jammed the left side of a bicycle front fork into it, and never changed it because it's quite comfortable.

I like a gas spring because it's damped and doesn't shoot off if the belt breaks. I believe it's also more linear than a coil spring. Here is the exact one I got, it's not very expensive: https://www.mcmaster.com/9416K11/

This photo is from a while ago, it's since moved to its own spot on a different bench.


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## devils4ever (Feb 22, 2021)

Thanks, but which one do you have? They list 15, 20, 30, 40, 50, 60, 70, 80 lbs extension force versions. I'm a little confused. They list extension force, but you really want compression force, don't you? You have to click on each to to find this out.


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## Masterjuggler (Feb 22, 2021)

I have the 80lb spring. I mentioned 85 before, that was a mistake.

I'm not really sure what you mean by extension vs compression force. Maybe I'm misunderstanding, but they are the same according to Newton's third law. The force it takes to compress is exactly the force it exerts, in the opposite direction.

EDIT: I think I see what you're talking about where it lists the "compression force." I believe that is the force when fully compressed.


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## devils4ever (Feb 22, 2021)

On McMaster-Carr website, it shows extension force as the determining factor.

See this. It shows Extension Force of 80 lbs at the top of the page and a Compression Force of 108 lbs in the details. So, what's that mean?


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## Masterjuggler (Feb 22, 2021)

I edited my previous post, but I guess not fast enough lol. I believe the "compression force" is just the force when fully compressed.


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## devils4ever (Feb 22, 2021)

Oh. So, it's 80 lbs of force when full extended and 108 lbs when fully compressed (both pushing the ends apart). Now, I get it.

I was thinking that there was an extension force like pulling a spring on the ends!


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## rwm (Feb 22, 2021)

I am glad you explained that. I may put one of these on my belt grinder also.
Robert


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## ttabbal (Feb 22, 2021)

Masterjuggler said:


> The one I did is EXCEEDINGLY jank lol.




If it spins the belt and grinds metal, it's good enough!   

Here's mine. I had fun with paint.


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## mikey (Feb 22, 2021)

What is that, leftover paint from your John Deere?


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## ttabbal (Feb 22, 2021)

My rocket actually...   

My kids like yellow and green.


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## devils4ever (Feb 25, 2021)

I got my motor, VFD, and wheels in. I'm trying to determine the cord to use. 

Is the correct wire 12/3 SOOW for the single phase 220V, 20A to the VFD and 12/4 SOOW for the 3 phase to the motor from the VFD? Or, can I use SJOOW for both or a smaller gauge?


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## jwmelvin (Feb 25, 2021)

The VFD wire should be shielded. They do make VFD cable, like this: https://www.wireandcableyourway.com/12-3c-w-3-16-grounds-shielded-vfd-cable


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## devils4ever (Feb 25, 2021)

Are you talking about the 220VAC single phase from the house to the VFD unit needing shielding? Or, the 3 phase cord from the VFD to the motor?

I've never heard of shielding being required.


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## jwmelvin (Feb 25, 2021)

The cable from the VFD to the motor is subject to a lot of high-frequency noise. As I understand it, the shielding will help prevent radiation of that noise. I’ve seen issues with the noise before, where wrapping each motor lead around a ferrite core helped tremendously.


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## ttabbal (Feb 25, 2021)

For 20A, 12AWG is fine. I think for a short run, 14AWG should be alright, but I like to oversize a little, just in case. I'm pretty sure SOOW is what I used. It looks like SJOOW insulation is rated for 300V, while SOOW is 600V. I don't think I'd be comfortable being right on the edge of the insulation rating for SJOOW. 

I don't use any shielded cable for my VFDs. In theory, there is electrical noise being emitted from the wires due to the way they generate the 3 phase. In practice, it hasn't bothered anything in my garage. Even the import DROs don't seem to mind it, and they seem to be the things most people see issues with. There's also that this is a grinder. It's not something that you are going to likely be running with sensitive electronics also in use. My biggest reason for non-shielded is that it was easy to get locally. The local HD had a remnant that was inexpensive as well, so I figured I wasn't out much if I ended up replacing it.


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## jwmelvin (Feb 25, 2021)

I will say that the machine I worked on with noise issues had a very long cable from the VFD to the motor. Like 15’. We didn’t have much experience.


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## devils4ever (Feb 26, 2021)

Okay, I bought 12/3 SOOW and 12/4 SOOW cord from Home Depot. The VFD has 2 size cutouts. I bought PG21 cable glands to seal the cables on the VFD and motor. The larger cutoff fits perfectly with a PG21 cable gland. 

But, the other one is causing an issue. The problem is the smaller cutouts are too small for the SOOW cable on both the motor and VFD. 

Here's the dimensions:
VFD and motor cutout diameters: 0.875" = 22.2 mm
12/3 SOOW cable diameter = 0.59" = 15.0 mm
12/4 SOOW cable diameter = 0.64" = 16.3 mm

*PG21 Cable Gland*
Cable diameter range: 0.51" - 0.71" (fits)
Threaded diameter: 1.11" (too big)

*PG16 Cable Gland*
Cable diameter range: 0.39" - 0.51" (too small)
Threaded diameter: 0.89" (too big)

*1/2" Trade Size*
Cable diameter range: 0.39" - 0.55" (too small)
Threaded diameter: 0.84" (works)

So, what does everyone use?

The 1/2" trade size is close to working, but still too small. The fact that the motor and VFD openings are so small makes me question whether 12 AWG cord is needed and whether SOOW (600 V) cable is needed. 

The motor datasheet does state 12 AWG, but makes no mention of the voltage rating. Other places on the Internet do show that 14 AWG is more than adequate for a 3 phase, 2 HP motor running at 220 V.

I plan on addressing any noise issues after the fact. Cough42 did a episode on this on his lathe VFD conversion, so I can use that as a guide. I plan on keeping my cables short between the VFD and motor.


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## ttabbal (Feb 26, 2021)

My VFD isn't sealed, so it just has flexible entry ports for the wiring. Could the ports for cable glands be metric? 

Voltage on the motor side is 220V. I personally like insulation to be rated for close to 2x voltage as "stuff" happens in real life that can damage insulation. It may be that I'm paranoid and it's a non issue. 

Wire size needed depends on current. Which depends on the motor. What's the motor plate say? It might list it as "FLA". I suspect it's likely low enough that you can use 14AWG. I think my 2HP motor is 11A, which would be fine for 14AWG.


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## devils4ever (Feb 26, 2021)

Looks like the motor current at 230V is less than 5 Amps (less than 6 Amps at SF 1.15). Strange since the motor manual recommends 12 gauge wire. Seems like massive overkill. I can see the need for 600V cable more than this gauge wire.

I already have 12/4 SOOW cord, so I'll guess I'll have to figure out a way to use it. It's not cheap even though I only bought a small amount. I ordered PG16 cable glands which will fit the holes in the VFD and motor. Maximum opening is 0.511". Cable is 0.64". 

Maybe I can open up the cable gland at the cost losing the water proof feature? I don't need water proof, but I'd like it impervious to grinding dust. That's the whole point of using these.


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## ttabbal (Feb 26, 2021)

I guess they could be concerned about startup surge currents. Not really an issue with a VFD as they generally soft-start. Even then I'm not sure you could get enough current to be a problem. But you have it and they recommend it, might as well try to use it. 

If you open one up and there's no rubber left, you could use some silicone sealant to seal it up. 

Not ideal, but would the 3 wires make it in without the outer jacket? You can connect the ground outside the motor itself. Maybe replace it with some heatshrink? With some careful setup, you should be able to even seal up the opening in the outer jacket from water incursion, not that it really matters in this case. It would protect the wiring from abrasion though.


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## devils4ever (Feb 27, 2021)

Well, I got it working. I removed the rubber seal from the PG16 cable gland which gave me a little more space. Then, I carefully sliced off some of the heavy outer insulation from the 12/4 SOOW cord. With some pushing and coercion, I was able to get the cord through. I'm not sure if it's a waterproof seal, but it's should be grinding dust tight.

 The opening in the boxes were a little tight for the OD of the cable gland, but I was able to push them in since they were plastic.

I fired up the motor and it ran great. The KBAC-19 (1P) 10001 VFD worked great and has no programming steps to go through. Every option is set by little shunts on the PC board. Very easy.

All right. On to the mechanics! With my design nearly done, I need to start order some steel!


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## devils4ever (May 7, 2021)

I'm just about done with my belt grinder project. What does everyone recommend for finishing? Caswell Black Oxide kit?


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## devils4ever (Jun 1, 2021)

Project done!!! This is after months of designing, material gathering, machining, fabricating, etc. I think it came out great. I tried to make it as beefy as possible to avoid flexing and deflection and I think I succeeded. With the 2X feature on the VFD, I can get over 11,000 SFPM. It's made of mostly 3/8" (~9.5 mm) 1018 steel. I made the base out of mostly 3/4" plywood and the top doors will open to allow access to my 6" bench grinder should the need arise.

I may add a glass platen in the future, but I'm leaving it as is for now.


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## Steve-F (Jun 1, 2021)

Really Nice!!!


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## 7milesup (Jun 1, 2021)

You big Devil, that is awesome!   Very nicely done.


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## nnam (Jun 1, 2021)

Very nice.  Do you mind share how you thought about the dust collection part when you designed it?  I thought that is a must have feature.


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## devils4ever (Jun 1, 2021)

I'm still looking into dust collection. I'm not sure how to implement it.


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## mikey (Jun 1, 2021)

So, how does it run? Are you happy with it?


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## devils4ever (Jun 1, 2021)

Runs great! I'm very happy how it turned out. It's rock solid and it grinds SO much faster than my 6" bench grinder.

Now, I can get back to learning how to grind HSS lathe tool bits!


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## mikey (Jun 1, 2021)

I suggest you epoxy on a platen liner now, before you dish your steel platen. I promise you that you will not regret this. If you can, drill and tap for two screws to support the liner before you epoxy it on. I suggest JB Weld.


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## devils4ever (Jun 1, 2021)

OK. I'll look into getting one. Do you have a good source for this?


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## mikey (Jun 1, 2021)

Sure, here you go.


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## rwm (Jun 1, 2021)

That is stunning! Looks super beefy.
Robert


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## WobblyHand (Jun 1, 2021)

mikey said:


> I suggest you epoxy on a platen liner now, before you dish your steel platen. I promise you that you will not regret this. If you can, drill and tap for two screws to support the liner before you epoxy it on. I suggest JB Weld.


I learned the hard way about the platen.  It only took a month or two before the platen was significantly eroded.  The ceramic glass platen is a very good thing to add.  I can't detect any wear on the glass platen.

Your grinder looks amazing.  Nice job.


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## projectnut (Jun 2, 2021)

WobblyHand said:


> I learned the hard way about the platen.  It only took a month or two before the platen was significantly eroded.  The ceramic glass platen is a very good thing to add.  I can't detect any wear on the glass platen.
> 
> Your grinder looks amazing.  Nice job.



Just what is it you guys are grinding that causes the platen to erode?  I have a Delta/Rockwell 6x 48 belt sander with a 12" disk.  I use it on a regular basis.  It's been in my shop for over 20 years, and both the belt and disk platen are in good shape.  The belt platen does have some marks on it where the previous owner ran it into the belt, but other than that it's in good shape.  I might add this machine was built in either the late 1950's or early 1960's, so it's been in use 60 years or better.


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## WobblyHand (Jun 2, 2021)

Grinding HSS lathe tools.  Platen was not hardened steel, just some sort of cast steel.  First the paint wore away, then the steel started getting divots.  For general use, and for wider pieces which reduce the contact forces, I bet a regular platen would last a long time.  For grinding HSS and cobalt tooling a ceramic glass platen is better.  Hey it's a sample of one, but that's my experience.


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## mikey (Jun 2, 2021)

projectnut said:


> Just what is it you guys are grinding that causes the platen to erode?  I have a Delta/Rockwell 6x 48 belt sander with a 12" disk.  I use it on a regular basis.  It's been in my shop for over 20 years, and both the belt and disk platen are in good shape.  The belt platen does have some marks on it where the previous owner ran it into the belt, but other than that it's in good shape.  I might add this machine was built in either the late 1950's or early 1960's, so it's been in use 60 years or better.


A lot of us use belt sanders for tool grinding that requires a truly flat platen to create a truly flat face on the tool. I know from long experience that I can dish out a steel platen grinding lathe tools in a week or less, whereas a glass platen will last for a decade or more without any significant wear.


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## projectnut (Jun 2, 2021)

mikey said:


> A lot of us use belt sanders for tool grinding that requires a truly flat platen to create a truly flat face on the tool. I know from long experience that I can dish out a steel platen grinding lathe tools in a week or less, whereas a glass platen will last for a decade or more without any significant wear.


That's interesting.  While I do use my Delta/Rockwell  grinder for a number of other things it's primary function is to either create new form tooling from HSS blanks, or to sharpen existing tooling.  It spent it's previous 40+ years in one of the machine shops at work providing the same service.  That's a total time of close to 60 years either sharpening or creating HSS tooling.

After reading a few posts regarding the platen dishing I went into the shop and put a straight edge across both the belt and disk platens.  I couldn't force an .001" feeler gauge between the straight edge  and either platen anywhere.  I have no idea what the platens are made out of, but they do carry the OEM part number so they are either originals or factory replacements.


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## Firstram (Jun 2, 2021)

Most 6x48 sanders don’t have the same belt speed as a 2x72, less heat. Could it be cast iron vs mild steel?


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## mikey (Jun 2, 2021)

projectnut said:


> That's interesting.  While I do use my Delta/Rockwell  grinder for a number of other things it's primary function is to either create new form tooling from HSS blanks, or to sharpen existing tooling.  It spent it's previous 40+ years in one of the machine shops at work providing the same service.  That's a total time of close to 60 years either sharpening or creating HSS tooling.
> 
> After reading a few posts regarding the platen dishing I went into the shop and put a straight edge across both the belt and disk platens.  I couldn't force an .001" feeler gauge between the straight edge  and either platen anywhere.  I have no idea what the platens are made out of, but they do carry the OEM part number so they are either originals or factory replacements.



I dunno', might just be that my belt sander platen was cheap junk steel but I had to replace mine too many times. In contrast, my first glass platen lasted over 11 years and remained dead flat despite grinding hundreds of HSS tools on it. I am now on my second glass platen and expect it to go for at least the next decade or more.


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## devils4ever (Jun 5, 2021)

I completed the glass platen mount. It is ready for the glass platen which should be arriving shortly.

I made the shelf 0.180" thick since the platen is 0.192" thick. I'm hoping that enough clearance. 

Also, I used 4-40 screws to hold the shelf in place. I'm hoping that's strong enough. I didn't want to go bigger since there would be very little material left from the countersink for the flat head screws.


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## mikey (Jun 5, 2021)

That should work fine. Be sure to rough up the platen and glass where they contact with some sandpaper before you clean and epoxy them together. I just use some 80 grit paper to put some scratches on them, blow off the dust and then clean with lacquer thinner before applying the JB Weld.

I use precision ground flat stock as a platen so I just used spring clamps to hold the platen and liner together. Some folks use tape, others just a weight and still others recommend no weight at all. The latter are using some not-so-flat mild steel and have experienced cracking of the liner when using clamps.


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## COMachinist (Jun 6, 2021)

I suggest you not glue or epoxy the glass to the platen. I use indoor/outdoor carpet double sided tape. I have had a few glass platen crack or break and changing them is a pain, oh and they will wear. I just use acetone to flip them over, and get double the use. They won’t go any where with the tape and the bottom ledge.
CH


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## Watchwatch (Jun 6, 2021)

COMachinist said:


> I suggest you not glue or epoxy the glass to the platen. I use indoor/outdoor carpet double sided tape. I have had a few glass platen crack or break and changing them is a pain, oh and they will wear. I just use acetone to flip them over, and get double the use. They won’t go any where with the tape and the bottom ledge.
> CH



+1

I used 3m automotive double sided tape. Works great and no mess. 


Sent from my iPhone using Tapatalk


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## 7milesup (Jun 6, 2021)

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## devils4ever (Jun 6, 2021)

I've seen conflicting reports between JB Weld and carpet tape. What to do???


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## mikey (Jun 6, 2021)

My first glass platen went 11 years before it let go from the backing plate and that happened only because my belt snapped and I assume it smacked that platen pretty good and knocked it loose. 11 years without a hitch, and it took a fair amount of abuse in my shop. I've seen guys on youtube mount platen liners with tape and RTV silicon and that's fine, their machine and their risk. For myself, I'll use JB Weld. I don't know if it is better or worse but I know what I'm comfortable with.

As far as I know, the vast majority of knife makers who use glass platens use JB Weld or some other epoxy, at least unless things have changed.


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## devils4ever (Jun 9, 2021)

I used JB Weld and it seems to be on there for good! I'm hoping I never need to remove it. It took a lot more of the epoxy than I thought. I kept making up more and more of it. But, it's done!


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## Buffalo21 (Jun 9, 2021)

As I have stated before, I don’t understand the glass platen need, I used numerous belt sanders/grinders, for years, with numerous machines (burr-King, Jancy and a few others, on a 40/hr a week basis. I’ve never had an issue with the platen wearing, belt overheating or belt life issues. My Burr-King is 30+ yrs old, it still has the original platen, some bearings and a motor, have been replaced.


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## WobblyHand (Jun 9, 2021)

Buffalo21 said:


> As I have stated before, I don’t understand the glass platen need, I used numerous belt sanders/grinders, for years, with numerous machines (burr-King, Jancy and a few others, on a 40/hr a week basis. I’ve never had an issue with the platen wearing, belt overheating or belt life issues. My Burr-King is 30+ yrs old, it still has the original platen, some bearings and a motor, have been replaced.


You are fortunate to have a good grinder with a quality steel platen.  I was not as fortunate.  Mine wore out in a few months.  My belt was only 2 inches wide and grinding 3/8" HSS or cobalt in a localized area did cause wear.  My platen was cast steel, not a quality steel.  I milled out a pocket and JB Welded in a glass platen.  It wasn't hard to do and gave better grinding results.  Sample of one.


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## Masterjuggler (Jun 12, 2021)

I personally use RTV silicone for my glass platen with a small ledge welded at the bottom to keep it from being forced downward. I see it as being similar to a laminated glass windshield, where even if I crack the glass, (I'm hoping) the shards stay stuck until I want them to come off. Short of that, a more flexible epoxy like west system g/flex makes more sense to me.


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## rwm (Jun 12, 2021)

Next step- get some of the green zirconia belts. Check Red Label Abrasives.
Robert


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