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How to enlarge/widen an existing keyway in drive wheel?


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Hi everyone. This is my first post. I'm just starting out in knife making, and so I'm collecting materials to build my first 4x72 belt grinder. 

 

I bought a set of wheels on eBay. Unfortunately, the seller didn't provide me with the product we both agreed to: I asked for a drive wheel with a 6mm keyway, and the seller provided me with one that is around 4.76mm wide (see pic). 

 

I opened a dispute on eBay and received a refund. eBay support were great throughout it all. I would have been happy if the seller had offered a partial refund, or if he had just sent me the correct size wheel, but he was uncooperative and rude... At least eBay themselves saw the problem and stepped in. 

 

Anyway - could any experts please tell me: is it possible for me to enlarge this keyway to the correct size, using only the basic tools I already have? I mean, I have files, dremel, etc. I actually have a small press, but not something huge like you guys probably have in your shops, so I'm not sure if I could broach it successfully. 

 

Obviously, the solution would appear to be to take a small file and just file it out, but I'm worried that the result won't be very accurate. Will that matter? Or will it still work OK? 

 

I'd greatly appreciate anyone's input here. Thanks very much. 

 

s-l1600-5.jpg

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A small flat file with a safe edge should work fine.  Use a piece of the key stock to check fit and go slow at it.  You have to work both sides of the slot evenly to keep it parallel or perpendicular to the radius

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A file will do it. As said, you will want a hand file (less than about 4mm thick) with a safe edge and you'll need to work on both sides evenly to keep things aligned.

 

Are there any grub screws in the pulley? If so, they'll make things a bit less critical in terms of slot accuracy. The bore provides the 90-degree alignment to the shaft, the key/keyway provides the driving force and the grub screw(s) prevent axial movement.

 

In essence, the likelihood is that you'll end up with a slot with convex sides (unless you are good enough with a file that you'd have just done it and not bothered asking the question) and the critical part will be that the narrowest section of the slot is a good enough fit on the key to drive it without play. 

 

If you get it pretty close, but not perfect, you can usually use Loctite (or one of the cheaper alternatives) for additional hold. I'd probably go with Loctite 290 or an equivalent "wicking" product, as it will allow you to get everything correctly aligned dry and then apply a few drops that will wick into the gaps and set up. There are other products, like Loctite 620 or 638, that are stronger retainers, but you'll need to apply these, assemble and get things aligned correctly pretty quickly if you use them. Don't expect to be able to easily remove the wheel if you Loctite it. 

 

 

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Fantastic. Thanks for the advice guys. 

 

Just measured it and realised I'll have to deepen the keyway too... It's about 2.2mm deep and I need 3mm for the key on my motor. I'll file it carefully and hope for the best. 

 

My main worry was that an imperfect fit would result in vibration. 

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As long as you stay in the keyway and use the Loctite you'll be fine.  I'd be worried if you were drilling the hole larger, but the keyway isn't as critical. 

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The right way to do this is to broach the keyway.  You will need a press (a small manual one will suffice) and a broaching kit.  This will size the keyway precisely.  I needed to do this on my homemade disk grinder.

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I think I'd file down the key to fit the slot depth, rather than file down the slot to fit the key depth. The key will come out and allow you to do the filing in a vice (vise) where it's easy.

 

I've done enough filing to know I'm not good at it. Using a safe-edged file to increase the slot width should keep you from chewing up the bottom of the slot by running the safe-edge on it. If you need to deepen the slot, the safe-edge moves out of the equation and your opportunities for lousing things up increase considerably because you are working in 3 dimensions instead of 2: think flying under a bridge vs driving under a bridge.

 

Once you've got the slot width right, using the loose key to check. it becomes a simple job to match the key depth.

 

 

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shape the key or file it or broach it you don't need a heavy press you can even use a hand hammer its not tool steel your broaching even a drill press can be used when i broached a slot i bought the bushing to match the bore and made a broach from the same stock i wanted to fit (think it was 304 ss) i just filed/ground it till it looked like a broach you will need shims to do the dead but there easier to make than the broach

Edited by dragoncutlery
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Brandon Sawisch bladesmith

 

eagles may soar but weasels don't get sucked in to jet engines

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23 hours ago, timgunn said:

 

I think I'd file down the key to fit the slot depth, rather than file down the slot to fit the key depth.

 

Thanks for the input. I thought about this, but figured maybe this would permanently alter the drive shaft of the motor so I could never use it with any other drive wheel... Or am I wrong here? I didn't realise that I might be able to remove the key from the drive shaft. If so then you're right, that might be the simplest solution. 

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15 hours ago, dragoncutlery said:

shape the key or file it or broach it you don't need a heavy press you can even use a hand hammer its not tool steel your broaching even a drill press can be used when i broached a slot i bought the bushing to match the bore and made a broach from the same stock i wanted to fit (think it was 304 ss) i just filed/ground it till it looked like a broach you will need shims to do the dead but there easier to make than the broach

I find this idea really interesting. I might be able to get some 6mm tool steel and make a broach, perhaps... I just assumed that broaches etc would need to be really precisely machined and that a massive press would be required. 

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6 hours ago, BenjaminSelby said:

Thanks for the input. I thought about this, but figured maybe this would permanently alter the drive shaft of the motor so I could never use it with any other drive wheel... Or am I wrong here? I didn't realise that I might be able to remove the key from the drive shaft. If so then you're right, that might be the simplest solution. 

 

You were thinking of filing down the keyway on the motor shaft?  That way lies madness. ;)  If you need to remove material, do it on the wheel (for width) or the key itself (for depth), as Tim suggested (always listen to Tim!).  And keys are indeed removeable. A tap with a soft mallet should do it.  Be sure to wrap it in several turns of rubber band/elastic first, lest it go flying into the aether never to be seen again.

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Alternatively, one could remove the key and modify it (or make a new one from scratch) to be T-shaped so that it fits the current keyways in both the motor shaft and the wheel.  This is much easier with a milling machine, but key stock is cheap and easy to come by, so the risk if it is messed up is pretty low.  A few scribed lines and a bit of careful filing could get you there.  

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4 hours ago, Alan Longmire said:

 

You were thinking of filing down the keyway on the motor shaft?  

Oh, ha ha ha - no way! No, I was initially intending to enlarge only the keyway on the drive wheel. I never considered reducing the size of the key itself on the motor. I figured it was a permanent part of the motor/drive shaft assembly. But some members here suggested that the key on the shaft could be filed down to fit the smaller keyway on the drive wheel, so now I'm thinking that might be an option (although to be honest I'd still prefer to alter the drive wheel itself because it's non-standard as it currently is). 

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I once cut a key way in a aluminum wheel with a sharp cold chisel.  Crude but worked. You are correct thinking that filing the key way in your wheel the best way.  It is aluminum so should go quickly.  Broaching would be best but you need the tooling.

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On 3/7/2022 at 3:24 AM, BenjaminSelby said:

I find this idea really interesting. I might be able to get some 6mm tool steel and make a broach, perhaps... I just assumed that broaches etc would need to be really precisely machined and that a massive press would be required. 

Not at the sizes your working if the broch is sized right each tooth is just shaving a bit of material at a time not 1/8 inch passes 

Brandon Sawisch bladesmith

 

eagles may soar but weasels don't get sucked in to jet engines

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Posted (edited)

Well, I considered a lot of the options presented here. Thanks very much to everyone for your input. I took a needle file to it and after over an hour of solid filing, I enlarged the keyway enough that the wheel now fits on the motor drive shaft. I had to tap the wheel a few times with a mallet to get it to seat on the shaft fully (not looking forward to the struggle if I ever need to get it off again...) It seems pretty sturdy and doesn't look like it will wobble/vibrate. I realise that my filing job is dodgy as hell but it seems ok for now. 

IMG_3389.jpg

 

Edit: I definitely considered the idea of making a broach, but I figured it would be a lot of work for something I'm probably only going to use once. It would have been an interesting experiment, though. 

Edited by BenjaminSelby
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