DIY Belt Grinder Build Questions

[ttabbal]

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.

 

[devils4ever]

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.

 

[ttabbal]

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.

 

[devils4ever]

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?

 

[rwm]

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

 

[Masterjuggler]

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.

 

[ttabbal]

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

 

[devils4ever]

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!

 

[Masterjuggler]

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.

 

[devils4ever]

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.