[4]

Could use some design help with a belt grinder

[3]
[10] Like what you see?
Click here to donate to this forum and upgrade your account!

MikeWi

Active User
Registered
Joined
Jan 21, 2013
Messages
497
I'm designing a 42" belt grinder to attach to the right side of my new bench grinder. it gives me something to learn Fusion 360 with :) I have no trouble designing things, but I have no engineering knowledge at all, so I'm never sure what is enough or too much. Almost everything I see on the net is made of 1/2 plate or similar heavy materials, but I want to use what I have on hand, and I just don't believe it needs to be that heavy. The whole thing is about 20" tall. I having a lot of fun, and the design is parameter driven, so I can make adjustments to one item and everything else adjusts to suit. Nice! This is mainly intended to be an additional tool for sharpening and shaping lathe tools and drill bits. My old 6" grinder will keep the gray wheels for doing anything else.

Anyway, the questions:
1) I'm planning on using a 4" drive wheel, which will get me around 3600 SFPM. From what I've found that seems to be reasonable. Any thoughts?
2) I'm struggling on the platen support. I'm currently looking at a 1/4" plate that will hold an 1/8" plate with pyroceram plate glued to it's face. To hold it out from the tower, I'm looking at 1/4 again, anchoring where the two tabs are projecting, with an option of further contact at the top of the grinder base. There will be adjustment for belt contact and angle. Do you think that this would be rigid enough?

here's what I have so far. Clearly still a work in progress. :)
snapshot.png
 

MikeWi

Active User
Registered
Joined
Jan 21, 2013
Messages
497
Well even that company's grinders only do 6000 in spite of that article. I've seen anywhere from 3600 on up, but I was wondering if anyone is using one here. I don't even know when I'd build this anyway, but it'd be a fun project for the lathe as well as my CAD practice.
 
D

Deleted member 43583

Guest - Please Register!
Guest - Please Register!
I have a KMG 2 x 72 that is variable speed. My top belt speed is a little shy of 5400 as I remember. Occasionally I feel that it would be nice if it was a touch higher.

I did some studying on belt speed recommendations by 3M and others and their answers kept coming out at 7000+ for their ceramic abrasives belts.
Not sure if you are planning for a variable speed drive or not. If it's fixed speed, I'd likely stick with the 3600.
 

mikey

Active User
H-M Platinum Supporter ($50)
Joined
Dec 20, 2012
Messages
5,547
Mike, if I was going to build a 2x42 belt sander, I would order the wheels from Sears that fit their belt sander. The lower drive wheel is 5". The upper wheel mount incorporates the tracking mechanism and it is simple and effective, and it bolts on to a flat chassis. For a chassis, I would use a single piece of 1/4" thick steel plate that mounts to the motor housing at the bottom. I would weld a stiffening piece (at the back of the vertical piece) and carry it under the lower wheel to stiffen the vertical piece.

The steel vertical chassis would allow you to easily mount an angle iron platen support (adjustable fore and aft to align with the belt) to which a ground steel platen can be mounted. A Pyroceram liner can be epoxied onto this platen and it would be very solid.

The chassis would also allow you to mount a tool rest solidly.

Okay, out of ideas.
 

MikeInOr

Active Member
Registered
Joined
Jan 1, 2018
Messages
259
My 4 x 72 belt sander has a piece of graphite impregnated material on the platen... it does a wonderful job. It has been there for 40+ years and probably has another 200+ years of home shop use left on it. My father originally used double sided tape to mount it... the tape strips eventually worked there way through the material and left lumps. I pulled up the material and replaced the double sided tape with contact cement... been working great since and the lumps flattened themselves out very quickly. I remember when my father first put the graphite impregnated material on the platen... it was like doubling the hp of the drive motor.

1/4" plate sounds plenty strong and ridged to me... I think the HarborFreight belt sanders use aluminum foil as their structural material.
 
Last edited:
F

f350ca

Guest - Please Register!
Guest - Please Register!
I've been considering building one too Mike. The speed thing seams to be all over the place. As Alan posted 3M recommends high speeds. Im inclined to think the belt might perform best at the recommended speeds. They make slow speed wheel grinders for sharpening carbon steel wood working tools but I can't imagine trying to remove much metal with them. An 8 inch grinder cuts a lot quicker than a 6 inch with the wheel rotating at the same speed. And that first section of the wheel wears a lot slower compared to the next inch once you've wore it down to say 7 inch dia and are running at a lower surface speed.
From their charts 6500 fpm seams like a good speed if your going to be operating with a single speed motor as I was planning. Thats the recommended speed for carbon steel and the low end for stainless and aluminum with fine grit belts.
Like you I'd appreciate some input from real world experience.
Im planning on 2x72 belt size, they seam to be a lot easier to find up here and expect they wear beter with the extra surface.

Greg
 

ttabbal

Brass
Registered
Joined
Jun 12, 2017
Messages
905
I haven't done a lot with mine yet. However, I read that ceramic belts work better at high speeds. My grinder runs off a VFD, so I can set it to many different speeds. I tried about 3000, it works but seems to make the part hotter. 6000ish removed material much faster and kept the part cooler. With a 36 grit belt, keystock is gone in seconds. For finishing work with aluminum oxide belts I expect slower speeds would be better.

Speeds are approximate as I don't have a tach, so I'm going by frequency from the VFD.
 

MikeWi

Active User
Registered
Joined
Jan 21, 2013
Messages
497
From whose charts exactly? I haven't found anything except a pdf from 3M that recommends 3500 to 4900 (roughly) for carbon steel. There are other places that state the higher speed ensures that the grit exposes new cutting edges and cuts cooler by taking the heat away in the chip. Many threads out there with the same confusion! LOL One source says that the "rule of thumb" for grinding belts is "a mile a minute" while the consensus among knife grinders is around 6000 sfpm.

I think I'll go higher with a larger drive wheel. I do like the idea of being able to use less pressure. That will keep wear and heat down.

There's been alot of comments I've read saying that 72 inch belts are the easiest to find, but I have no trouble finding any size. This place in particular seems to have anything you could want. http://www.trugrit.com/index.php?main_page=index&cPath=1_145
 
F

f350ca

Guest - Please Register!
Guest - Please Register!
The numbers I was quotng were from a 3M pdf as well Mike, didn't book mark it just wrote the figures down. Could be these were for ceramic and not aluminum oxide. They also gave belt tension 15-20 pound per inch of belt width. Wonder if aluminum oxide needs slower speeds, more research in order.

Greg
 
B

Buffalo20

Guest - Please Register!
Guest - Please Register!
My Jancy 2” x 42” is 3600 fpm, I also have a Burr-King, that variable from 3000 - 6000 fpm, I actually prefer the Jancy
 

rwm

Active User
H-M Supporter - Gold Member ($25)
Joined
Mar 25, 2013
Messages
1,701
Mike- nice work on Fusion. That is complex and beautiful.
I built a 2 x 42 that runs at about 5000 SFPM. It works fine but, I wish it were a touch faster.
I noticed you have all 3 pulleys crowned. I believe it would be better to have just the tracking pulley crowned and the others flat. It is important that the vertical post not flex or move. I think you have that covered.
Here's a pic of mine unfinished that shows the drive:

1518292169994.png

1518292217626.png
R
 

MikeWi

Active User
Registered
Joined
Jan 21, 2013
Messages
497
I noticed you have all 3 pulleys crowned. I believe it would be better to have just the tracking pulley crowned and the others flat. It is important that
I wasn't sure about that detail, thanks. Less work that way too.
 
F

f350ca

Guest - Please Register!
Guest - Please Register!
I've got into discussions about crowning pulleys for flat belts. A really old Machinists Handbook says to only crown one or the belt will hunt.
Nice design rwm. Im tight on space so was planing on making mine a two wheel one to reduce the depth.
Greg
 

MikeWi

Active User
Registered
Joined
Jan 21, 2013
Messages
497
Nice design rwm. Im tight on space so was planing on making mine a two wheel one to reduce the depth.
Greg
Thanks, I started with three because it was going to be a 60" belt, but discovered it would take up more room than I want. As is, the height is good I think. Since I'm going to go with a larger wheel, I'll have to look at the setup again.
 

rwm

Active User
H-M Supporter - Gold Member ($25)
Joined
Mar 25, 2013
Messages
1,701
The other question is direct drive or belts. If you go direct you need a 6-7" pulley at 3450 rpm. If you use belts you can run a slower motor (1725) or a smaller drive wheel and use pulleys to get the correct SPFM. That's what you see done on a lot of these. Burr King seems to prefer a 2:1 drive. I like the simplicity of the direct drive.
Also, think about some type of enclosure to hook up dust collection if you have it.
Robert
 
Last edited:

MikeWi

Active User
Registered
Joined
Jan 21, 2013
Messages
497
It's meant to mount directly to the grinder and stand. I still have to true up that side of the grinder and if I can't get rid of all the run-out, I may resort to in-direct to remove vibration. The pulley size depends on the SFPM issue we've been discussing, but I have changed to a 6" drive pulley now. Gotta love parametric CAD, change the pulley size, and everything else changes to suit. Hoods and such still have to be added.
 

Winegrower

H-M Supporter - Silver Member
H-M Supporter - Silver Member ($10)
Joined
Jul 29, 2014
Messages
315
I am having a failure of imagination about how I'd use something like a 2"x72" grinder. Would somebody please explain some typical things done with these tools?
 
S

SCLead

Guest - Please Register!
Guest - Please Register!
I am having a failure of imagination about how I'd use something like a 2"x72" grinder. Would somebody please explain some typical things done with these tools?
Very common among knifemakers. I'm sure other industries love them as well.
 

ttabbal

Brass
Registered
Joined
Jun 12, 2017
Messages
905
I use mine mostly for HSS lathe bit grinding. Other grinding jobs work well with it as well.
 

Winegrower

H-M Supporter - Silver Member
H-M Supporter - Silver Member ($10)
Joined
Jul 29, 2014
Messages
315
Thanks for the thoughts, Sclead and ttabbal. Knives, big ones, I could see...tool bits I can do well on my much smaller disc and belt sander. Maybe I should get one of these anyway? :)
 

ttabbal

Brass
Registered
Joined
Jun 12, 2017
Messages
905
I tried a smaller belt sander with a ceramic belt. Slow. With my 2x72 I can grind the angles in a few minutes on 3/8 cobalt bits. It's not really about the size of the part, it's how quickly and accurately they can grind.
 
[5] [7]
Top