Another dumb question

[vikingGoalie]

So, i'm very slowly starting to get my head around my workshop, what's needed, what i'm doing, etc, etc.
So my 1x42 old as heck craftsman sander does work. But it's very slow process, I can't press too hard as it will stop the motor dead.

Since my budget right now is meager, and I want a better grinder (and honestly my meager skills do not warrant a huge expenditure right now) I've started down the road of making my own 2x72 grinder.

I already have a donor tread mill with a 2.75 peak/2.0 continous HP motor and variable speed control.
Now my first question is.
I always see steel as the material in videos for the platen. I am assuming that is mainly for heat reasons. But I have to ask anyway, so a treadmill typically has a really high density melamine board under the running deck it's very low friction. So just how hot does the platen get on a "real" grinder. I know with my 1x42 it's no where near hot enough to be worried about combustion of wood.

I see this as a problematic thing and will most likely just end up using steel but had to ask

Next dumb question. So I'm keen on being a mad inventor, and I was going to re-use the rollers from the treadmill but I need more then just 2 rollers to make this sander.
I was looking at one of these: https://www.harborfreight.com/132-l...umjjFxjgvp6nHqyhvnLpKNWDTGbHDWoMaArwtEALw_wcB

because I already have one and they are like 13 bucks. A wacky idea I had was that I could cut that down some and the fact that it has an extension arm to adjust the length makes a lot of possibilities possible. BUT not sure now well that roller would stand up to continuous high speed revolutions. But I just might experiment some with it. I'm still noodling this all out in my head. I don't have any welding tools or experience so that makes some of the plans I've seen a bit harder to pull off.

anyhoo hope everyone has a great 4th...

 

[Alex Topfer]

I think the platen issue is more wear resistance. My steel platen has some visible wear after a year and a bit.
It does get hot, and might cause the glue in melamine to delaminate.

 

[Drew Riley]

I'll just throw a few thoughts out there, and you can take them or leave them.
I wouldn't try to re-invent the wheel too much when it comes to building a grinder. I don't see melamine board lasting too long as a flat platen. Even mild steel wears quite rapidly. The best material you can use for a platen is pyroceramic glass (aka pyroceram, robax, etc....). It's very low friction and will actually wear slower than hardened steel. The next best option is just that: hardened steel.
Grinding steel on a flat platen generates a lot of heat and friction on BOTH sides of the belt.

Concerning your treadmill motor, I know a lot of guys use them, but it's generally a short term solution, especially if it's an open frame motor. I mean, if it's free, and the treadmill is already in pieces, then go for it I guess, but if it were me, I'd sell the treadmill and put the money towards a used/surplus 3 phase motor and a cheap VFD. I've seen a lot of guys spend all kinds of time, effort and money trying to retrofit a treadmill motor to a homemade machine, only to burn multiple controllers and/or the motor, and by the time it's all said and done, they could have already had a decent 2hp motor and a VFD for the same money and less effort.

As for the roller stands, I wouldn't bother trying to use them for idler wheels. Search eBay for 2x72 idler wheels, or a lot of grinder manufacturers sell just the aluminum idlers. Prices average around $20 to $25 per wheel. I think Ameribrade sells them for $25 each, and they also have hardened steel platens for not a lot of money either, IIRC.

Last thing I'll throw out there: There are more options for grinder kits, parts, and/or machines than there ever has been. You can pretty easily get into a full working machine for around $1000, give or take. Reeder products sells a chassis, Housemade.US sells a kit... there's a hand full of others. I'd stay away from OBM/Diktator, but that's me.
Even if you decide to build your own, I'd still buy certain parts like the tracking, drive and idler wheels, as you can usually buy them cheaper than you could make them, and they'll likely be better quality.

The nice thing about investing into a decent 2x72, is 1) you can use it for much more than knife making, and 2) if it ends up not being your thing, you can likely sell it pretty readily for pretty close to what you paid for it, or at the very least, the amount of money you might have to knock off the sale price will be far less than you'll likely have tied up in a homemade "from scratch" build.

Hope this helps!

 

[Seedy Lot]

Soft steel platen quickly dishes, hardened steel much slower, ceramic glass best of all.

I see all kinds of issues with laminate board as a platten but I could be wrong.

 

[FredyCro]

Budget option for the platen is a regular bathroom ceramic tile cut to dimension and epoxied to a flat surface, preferably thick alu or steel.

Budget option for the wheels are skateboard wheels.

If I really had to do it on an absolute budget I would weld a steel tubing frame. Drive wheel can be made from laminated wood.

Or steel tubing frame made from offcuts, wheel set from eBay around 100, motor from crag list around 50 (and Chinese vfd around 80 optional).

 

[Stacy E. Apelt - Bladesmith]

All the things the other chaps said and a few more things.
That treadmill motor may say 2HP, but it isn't. Look at the specs plate on the treadmill and you will see that it draws around 600 to 700 watts. That is well under 1HP. Part of that is the controller, so the motor may only be 3/4HP.
Also, a treadmill is made to turn all the parts slow. At top running speed it is moving at about 1000 FPM. Most folks walk on a treadmill at 500FPM. Grinders run fast. at normal grinder speed, they run at 3000-4000FPM, which is 45MPH. Many folks grind at 6000FPS.
The rollers are also made for slow speed. Just like the melamine bed, they would get destroyed quickly on a belt grinder.

To wrap it up, either save up and buy a proper grinder frame and add a motor package (Reeder is a great starter chassis kit) or just use a cheaper 2X42" belt sander. You can get started with files and a stack of sandpaper.

Vilking - fill out your profile so we know where you live and a bit about you. It will help us give a better answer. It also may allow a local knifemaker to offer an old machine that needs some repair, some supplies and material, a spare motor, and some training in a good shop.