Capabilities: Is a 1 hp PM mill enough for 18-8 stainless steel? Or 2 hp?

[ErichKeane]

Thank you again everyone for all the super helpful info and support to the new guy. So much to read and so many videos to watch!

Here's where I'm at:

As far as PM bench mills go, the PM-833 is looking more and more like good fit for me. After seeing and hearing all of your feedback regarding working with 304 or 18-8 stainless, I think it would be best to stay in the 2hp camp no matter what style I end up choosing, and take the 1hp PM-728VT out of the running. Besides, the PM-833 seems to have just so much more to offer at a price increase that's within my budget. That being said, some of the drawbacks/limitations of this machine that I can see are:

1) Lack of a power down feed on the quill. I'd definitely opt for the power Z lift at time of order, but from the literature you've been providing, not having that quill down feed essentially takes boring operations off the table, at least not without some serious modification.

2) Lack of a power Y feed option. Not having a proper/steady feed rate could introduce difficulties when dealing with harder materials beyond aluminum. Not even having this as a future add-on option seems like a serious limitation to me.

3) I noticed in one of the videos that the y-direction table dimension on the PM-833 is 8-1/4 inches, compared to a common knee mill's 9+ inches. Correct me if I'm wrong, but I think this smaller dimension wouldn't allow me to mount a 6" vise horizontally, running the long way in x-direction. Is this a major disadvantage?

4) Nod adjustment will be a bit more challenging. I was hoping this to be a one-time set-and-forget thing, but I'll need to get my shims ready.


Regarding the knee mill option, it seems like just about everyone either ends up upgrading to one anyway, or highly suggests just biting the bullet right from the start and passing on the smaller machines. And to be honest, I can see why. Bridgeports and their clones have so much flexibility in what they can do, how easy it is to find replacement parts for them, and how well they hold their value. As a lowly woodworker and hobbyist though, I'm still not fully convinced that they're a perfect fit for everyone. As far as overall cubic volume and weight, many bench mills sit at about half their counterparts in both categories. For lighterm users and space-challenged individuals like myself, these are legitimate concerns when deciding on how much machine is really needed and how much machine we want hanging around our shop. What's a MAJOR bummer though is that these smaller, less capable bench mills are not half the price of the better used machines (i.e. BPs & clones)! From my shopping research, dollar for dollar, a used BP clone is equal to or less than a new bench mill. I think it's worth pointing out though, there is one key word difference here -- "used". As a newbie, knowing very little about metalworking, having the ability to differentiate between what's a "good" or "bad" machine in the world of used equipment is a serious gamble. Having no clue what I'm doing, then plopping down $6k on a piece of used equipment with absolutely no warranty or recourse of any kind, can be a scary proposition. If you have someone experienced enough to go shopping around with, that's great, but not everyone has access to that resource. Just sayin', there may be a method to all that "rookie madness".

It'll be fun looking back at this post 10 years from now. I'll probably cringe and smack myself in the head!

For #1: The lack of a power-quill 'stinks', but isn't a deal breaker. You can still use a boring head with manual feed, I did that a bunch on my millrite. You end up getting pretty good at feeding consistently

#2: Power Y can be added after the fact, but most of your operations are probably going to be feeding X anyway. My mill doesn't have Y, and I don't have a problem with it. Worst case, you get good at manual feeding.

#3: Thats DEFINITELY small compared to a Knee mill, ~12-15 is common in knee mills. That said, you'd have no problem mounting a 6" vise either direction, its a pretty good sized table. HOWEVER, with a mill that size, a 6" vise is going to be pretty crowded. I had a Millrite (which had a slightly bigger table), and always felt like the 6" was a bit too large.

#4: The lack of nod was one of the reasons I got rid of my millrite. However, it IS a once-and-done thing, and is likely easier on the 833 than the millrite.

I suspect you'll likely be happy with the 833 for quite a while. Its a little less capable than a knee mill, but not horribly so. You'll take lighter cuts, but still be able to get the same accuracy. You'll have a somewhat smaller envelope, but that is rarely a problem for most folks. A knee mill is GREAT, particularly knowing you can cut anything you want at any time. BUT, unless you're really concerned about the time (or if time is money!), a couple of extra passes isn't a big deal.

AS Far as price: you're right, you have to spend ~2x to get into a nice new bridgeport clone (even a 9x49). I would perhaps suggest getting as much as you can out of the 833, and keep an eye on craigslist/et-al for a while and see if you can find a cheap bridgeport someday (again, if you're wiling to dedicate the space!).

 

[Gladiataar]

So after all that rambling in my last update, I actually do have another question to throw out there on the topic:

Given my 80% aluminum, 20% stainless steel desired usages, as stated in my original post, which of the two motor choices would you recommend? Originally, I thought the belt driven PM-833TV would be the way to go, simply due to the wider speed range (50-3200rpm) offered, but now that I'm seeing how taxing 304 stainless can be on a mill, would the geared-motorhead on the PM-833V be the more practical way to go? I mean, according to one of the charts you guys provided, my available torque drops below 50% in those lower speed ranges. That sounds pretty significant to me. Conversely, how much rpm do I actually NEED to mill aluminum without breaking expensive bits? To my understanding, the issue lies in utilization of smaller diameter bits at lower rpms, but is that just because someone is wanting to increase the feed rate too much? Or are small diameter bits just not physically capable of milling aluminum in the sub-1500 rpm range without experiencing frequent problems?

I saw a video of some guy upgrading his motor to compensate for the lower rpm shortcomings, but it also looked like he had to add quite a bit of additional speed monitoring hardware and electronics to compensate for the difference in motor hz vs. spindle hz, or something like that. My point is, it didn't look like a simple or trivial "drop-in" procedure when upgrading the PM-833TV motor to achieve those better torque specs at lower rpm.

 

[ErichKeane]

IMO, you absolutely want the TV head. I don't really think you're going to be particularly torque limited, and if you find yourself torque limited, you can limit your DOC (probably only an issue with the 304).

50 RPM is plenty low enough, but there is no such thing as too much speed! 1500rpm out of the T head is too little. For HSS tooling, there IS no 'minimum' RPM, though carbide there is. However, smaller endmills/drills are TERRIBLE to use without sufficient RPM. The problem ends up being that what breaks an endmill/drill tends to be 'feeding faster than the cutter is able to cut material in front of it'. With bigger mills, you can feel this happening, however running something like 1/8" mill, or a #40+ drill without a ton of RPM means you're going to not feel it, and just snap it right off.

I have a 1/8" cutter that if I run at 1500 RPM will snap if I feed it any faster than a crawl. At 2200 RPM (max of my millrite), takes only a moment of feeding too quickly to cut off. At 3000 RPM on my new mill will cut all day as fast as I dare to feed it.

If you're doing a lot of aluminum, speed is going to be key to nice surface finishes. Get the 3200 RPM head! The lesser torque is going to be sad, but the only time you're cutting at sub-~400 RPM (particularly on Aluminum!) is with a big cutter: at which point you'll want a fly cutter anyway on a machine this size.

 

[ErichKeane]

One thing you might use to convince yourself: Grab the FSWizard Pro app for Android. The F&S calculator for it is a god-send for me. I punched in 6061-T6 with an HSS cutter. It suggests 229 RPM for a 10 INCH 4 flute endmill! Even a 1" endmill (bigger than your machine should ever run!) wants 2300 RPM.

For 304 stainless with an HSS 4 flute endmill, a 1/2" endmill wants 229 RPM, and you're way over a 1' endmill before you get sub-100 RPM.

 

[davidpbest]

From your post, it looks like you've been absorbing the feedback and coming to a good conclusion. I'll add a few additional comments inline below.

1) Lack of a power down feed on the quill. I'd definitely opt for the power Z lift at time of order, but from the literature you've been providing, not having that quill down feed essentially takes boring operations off the table, at least not without some serious modification.

It's not that you can't do boring operations, it that the tolerances you can achieve without power downfeed on the quill will be more sloppy. To do boring operations on a benchtop, you will need to move the head downward rather than the quill

2) Lack of a power Y feed option. Not having a proper/steady feed rate could introduce difficulties when dealing with harder materials beyond aluminum. Not even having this as a future add-on option seems like a serious limitation to me.

Power feed on the Y is a nice convenience but not a requirement. With my RF-45 I had for 15 years, I had power feed in the X-axis but not the Y-axis and got along fine. When I got the knee mill, it was more of a "well why not" get the Y-axis power feed that anything else.

3) I noticed in one of the videos that the y-direction table dimension on the PM-833 is 8-1/4 inches, compared to a common knee mill's 9+ inches. Correct me if I'm wrong, but I think this smaller dimension wouldn't allow me to mount a 6" vise horizontally, running the long way in x-direction. Is this a major disadvantage?

You should have no issue with a 6" vise in either direction. The table on my RF-45 was slightly smaller than the 833 and I ran it with dual 6" Kurt vises all the time. Comparison below - RF-45 on the left, PM-935 on the right:

4) Nod adjustment will be a bit more challenging. I was hoping this to be a one-time set-and-forget thing, but I'll need to get my shims ready.

With the benchtop, it's very unlikely you will throw off the nod once the machine and column are aligned. The tilt is easily dialed in at any time.

As a newbie, knowing very little about metalworking, having the ability to differentiate between what's a "good" or "bad" machine in the world of used equipment is a serious gamble. Having no clue what I'm doing, then plopping down $6k on a piece of used equipment with absolutely no warranty or recourse of any kind, can be a scary proposition.

That's exactly how I felt when I was in your situation. You'll be challenged enough getting a new mill set up and aligned properly without taking on aspects of wear and potentially broken components at the outset.

It'll be fun looking back at this post 10 years from now. I'll probably cringe and smack myself in the head!

The used market for quality benchtop mills is pretty robust. You can always upgrade later if you feel the need. At least half of my investment in milling is tooling and fixturing related anyway (rotary table, vises, all the cutters, collets, metallurgy and measurement tools, etc.) and all of that transfers from machine to machine so long as you stick with R8 tooling.

Given my 80% aluminum, 20% stainless steel desired usages, as stated in my original post, which of the two motor choices would you recommend? Originally, I thought the belt driven PM-833TV would be the way to go, simply due to the wider speed range (50-3200rpm) offered, but now that I'm seeing how taxing 304 stainless can be on a mill, would the geared-motorhead on the PM-833V be the more practical way to go?

In your situation, the TV is absolutely the right choice. Torque is not going to be your limiting factor given what you've said about the materials you'll be working with - rigidity will be your limitation with ether version of the 833 or the 935. If you were saying you wanted to power tap 4041 at 3/4" or run a 4" face mill at 0.100" DOC in stainless, then that's a different matter. But it doesn't sound like you will be HP or torque limited by the 833TV, and given your percentage use of aluminum, you will be glad to have the additional (3,200 RPM) top-end speed of the 833-TV. At 150 RPM and higher, the 833TV has enough torque and HP for your application as illustrated by the following videos of an 833TV in use on steel (A36 mild steel and 304 stainless are not very different in HP and torque requirement):

You might want to consider sticking with 4-flute carbide end mills for your stainless work. I typically run a 1/2" 4-flute uncoated carbide end mill at 800 RPM which is right in the sweet spot of the 833TV, and at 0.100" DOC, 75 percent tool engagement, a feed rate of 6 IPM. If you are doing a lot of 304, you will want to get a good feeds & speeds calculator for your smartphone (I use FSWizard), and having a DRO that displays your feed rate is worth whatever extra it costs over one that doesn't display feed rate. Machining stainless is much less forgiving in terms of getting your feeds and speeds dialed in, and you will want some kind of chip evac system like a Fogbuster or similar MQL coolant system (see the attached PDF).

 

[7milesup]

Once a BP or clone is on the cement in a garage , 2 people can move it without breaking a sweat . If space is an issue as you say , maybe the new smaller machines would be the choice . When it comes to $$$$ investing and work envelope , a used BP or clone will never lose money . The new machine as you say would most likely lose 40-50% the day you bought it .

That is totally incorrect. I had a PM833T for 5 years and sold it for $1200 more than I paid for it. The cost of machines goes up all the time and that is reflected in the used market.

 

[projectnut]

That is totally incorrect. I had a PM833T for 5 years and sold it for $1200 more than I paid for it. The cost of machines goes up all the time and that is reflected in the used market.

I think your experience is an exception. I've seen quite a few similar style mills for sale in the last 10 years that have an asking price in the neighborhood of 50% of the original cost. I don't know what they actually sold for, but I can't believe the buyers paid more than the asking price. A couple of the used equipment dealers I frequent won't even purchase that style mill unless they get it for close to nothing or already have someone looking for one.

On the other hand, I've had a Bridgeport for over 20 years and the asking prices for the same machine today are more than double what I paid for mine. Again, I have no idea what they actually sold for, but I doubt the seller went down to 50% of the original asking price.

 

[Larry$]

I would LOVE to have 3-axis DRO, but it's an $1100 option with PM.

I bought an Easson DRO and installed it on my Jet knee mill. Same brand as what my PM1440 came with. it serves me well and for a lot less than $1K. Takes some time to install as I had to make brackets beyond what it came with.

not having that quill down feed essentially takes boring operations off the table

Not true! I think you could manually do it. Power down certainly makes it easier/ more uniform.

2) Lack of a power Y feed option. Not having a proper/steady feed rate could introduce difficulties when dealing with harder materials beyond aluminum. Not even having this as a future add-on option seems like a serious limitation to me.

I don't have Y feed but can manually feed that direction if so inclined on any material. Using two handed feed, works OK.

wouldn't allow me to mount a 6" vise horizontally

Not sure why you'd want to but it would be a PIA to operate the vice that way. I've got a 6" Kurt mounted conventionally and take it on and off ass needed. My used mill came with a POS import vice that was a hazard. There are Kurt knock offs that seem to work well for others.

"good" or "bad" machine in the world of used equipment is a serious gamble

Yes, I've been through that when I went to buy a lathe. Spent a year looking, finally bought new. I'm in an area with a very limited used market. PM is good to deal with and worth paying a bit more for. I ordered my lathe in April 2016 and got it in October after several delays. It is Chinese, OK but not ideal. Go for Taiwanese if you can. Prices have gone up a lot since 2016! To compensate things that came "standard" then are options now.

 

[B2]

@Gladiataar

3) I noticed in one of the videos that the y-direction table dimension on the PM-833 is 8-1/4 inches, compared to a common knee mill's 9+ inches. Correct me if I'm wrong, but I think this smaller dimension wouldn't allow me to mount a 6" vise horizontally, running the long way in x-direction. Is this a major disadvantage?

The vise jaw width is not the only size dimension to pay attention too. Some jaws open wider than others. Then there are the other physical dimensions.

Some vises have a rotating base so you can rotate the bolt slots to match the table slots. This has advantages and disadvantages. However, this means that the non-rotated vise base part may hang off of the table front or back. Disadvantage of mounting the long vise axis along the x-axis is that it is hard to crank the handle on the vise when the handle cannot hang off the front or the end of the table. You would have to rotate in 1/2 turns re-position the handle and turn again.

Also, depending upon the Mill, the space at the back of a large vise can be an issue when mounted with the long axis along the y axis direction. It may limit your y-axis travel. Most of the vises have a coolant channel to guide the coolant onto the table for collection. This may stick out in the back a bit, especially with the rotating base, and my hang off of the table .... hitting the z-axis column or its cover etc.

By the way, my PM HAV-6 inch vise weights 41Kg, about ~90#. As I get older it is getting harder and harder to lift. I try very hard not get in a situation where I need to sit it down below waist level!

Dave L.

Edit: By the way, I do not know if other vises are built the same as the HAV-6, but the jaw face bolt holes are through holes, or atleast on both sides. This is kind of handy if you want to bolt anything to the back of the vise. I rigged up a big, 1/2" thick, plexiglass plate at the back and bolted hit here at the vise. This way the plate moved with the table without it being bolted to the table. Then I attached more plexiglass a the ends and from these I made a front to a plexiglass to form a bottomless box and lined it with heavy duty aluminum foil to catch the flood coolant and hot steel chips splattering from a large, long, job I was doing. Flood coolant really is messy, but it keeps things cool when the tool is actually submerged. I actually put door hinges at the plexiglass corners for easily dis- and assembly. I also mounted some cardboard onto the plexiglass to make it easy to adjust the height of the card board box sides to the working min z-axis travel. Then a temporary lid at the sides to keep "all" of this debris confined to the inside ... to some degree.

 

[davidpbest]

@Gladiataar

The vise jaw width is not the only size dimension to pay attention too. Some jaws open wider than others. Then there are the other physical dimensions.

You might want to have a look at this video which shows the flexibility of a Kurt 6" vise in terms of trampoline-type fixturing.