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Black Forest
08-25-2011, 06:01 AM
I am getting close to getting my little belt grinder done.
I don't have a vfd on it yet but I will soon.
It is 3hp and runs very good.

I made the drive wheel myself. It is 180mm diameter and 52mm wide out of steel. I only made it out of steel because I had the steel. I will probably get a rubber contact wheel for the drive wheel.
http://i853.photobucket.com/albums/ab91/burnandreturn/beltgrinderback.jpg
http://i853.photobucket.com/albums/ab91/burnandreturn/platenandtable.jpg

Tony
08-25-2011, 09:50 AM
My reply disappeared?

But what I said was: Nice JoB! and how fast does that spin your
belts? (SFPM?)

sasquatch
08-25-2011, 10:14 AM
Looking good.

The main verticle upright, how thick is that , it appears to be about 1/2 inch plate?

Any vibration problems?

sasquatch
08-25-2011, 10:20 AM
Forgot to ask,, the green machine in the back with the control knobs, what is that?

Thanks.

gwilson
08-25-2011, 11:35 AM
Black Forest,you may find that the back plate(platen) needs to be the same width as the belt,or it will not let you grind something like a step, which needs to be ground using the very edge of the belt.

You will also find that the bracket,which you have welded to the SIDE of the platen,will get in your way when you need to grind a step on that side of the belt. It is a PITA,but I suggest that you contrive to make bends in the support piece I refer to,and weld it to the BACK of your platen. That way,you have full access to grind on either edge of the belt.

If you will look back at the pictures of my Bowie knife,look at the way the grinds are terminated. The edges of the belt were needed to terminate the grind(though,in that case,the edges of the contact wheel were used).

The platen will soon get worn. I made a fully hardened plate of A2 steel,with 4 holes in it. One in each corner,countersunk on BOTH sides. This is bolted to the soft platen,and can be turned over when it gets worn. Another can be made when both sides get worn. The fully hardened A2 is pretty slow to get worn. On my Wilton Square Wheel grinder,the cast iron platen got worn fairly soon,and years ago,a new one was $100.00. Cast iron will last longer than your mild steel one,too. I just made the A2 wear plates instead of buying new platens periodically. I was able to machine the cast iron platen once or twice,to get it flat again,but it soon got too thin. Wear plates are better.

Black Forest
08-25-2011, 02:08 PM
THe plate is 10mm thick. Do you think it is too thin?

The green machine is my band saw.

I calculated I am getting 5200 SFM. I have a 80 grit belt on there now.

Black Forest
08-26-2011, 11:46 AM
I changed the platen as suggested. Nothing fancy but it is much better.
http://i853.photobucket.com/albums/ab91/burnandreturn/Platen1.jpg

Tony
08-26-2011, 12:55 PM
5200 sounds a little fast. You're grinding metal with it right?
I think mine is 3000 and it still feels fast. I have no speed control.

Tony
08-26-2011, 01:08 PM
Not to hijack your thread.. but here's a quick question for everyone
thats following.. and maybe might lead to improvements in yours..

but on mine, no matter how taut I make my belt, if I take anything more
than light passes (light pressure) I tend to round my leading edge. Hope
this drawing makes sense:

http://img.photobucket.com/albums/0903/knucklehead/grinder_rounding.jpg

the red line is my belt.
the purple line is what I *think* is happening.. its quite exaggerated
in the drawing.. in reality it looks flat as always.

My platen is positioned maybe 1/16" forward of the belt plane.

I've always wondered if it wasn't a function of my platen?
Maybe it should have some UHMW on it? Its just a piece of flycut
CRS.. perhaps too much friction?

Or my tensioning system just can't get things tight enough?

Or I'm expecting too much from a belt grinder. :)

gwilson
08-26-2011, 01:28 PM
Yes,there is always that annoying slight rounding no matter how tight you get the belt,at least when grinding with the flat platen. No such problem when grinding against the wheel,though.

I may have mentioned,when I wanted to make the Bowie knife I posted,I wanted to simulate the old knives,which were ground on very large diameter grinding wheels. I ground a block of steel with a slight radius on its face,and welded an arm on it to screw it against the flat platen from behind. It works great. The belt just runs around the curve on the steel block,leaving a much less hollow grind on a blade.

The block of steel is about 3/4" thick,partly bandsawed to a curve,then belt ground to a finished curve.

Black Forest
08-26-2011, 02:16 PM
I made two knobs to go on the bolts that hold the table and platen in place.

The back two bolts don't need a knob or nut. They are just there to position the two in the right place.

This was my first try at making anything like this so be gentle!
http://i853.photobucket.com/albums/ab91/burnandreturn/Knob.jpg

bborr01
08-26-2011, 02:29 PM
Forgot to ask,, the green machine in the back with the control knobs, what is that?

Thanks.

I think that might be his $5,000 coffee maker.

Brian

Elninio
08-26-2011, 05:01 PM
Does the rounding effect still happen if the pully on the top has more friction than the pulley on the bottom?

DATo
08-26-2011, 06:57 PM
Very nice job Black Forest !

gwilson
08-26-2011, 07:14 PM
The rounding effect on a machine like the Wilton Square Wheel grinder,where you can get the belt pretty tight,is minimal,but still there. You can only get the belts so tight,or their seams will tear loose. Those belts are violent when they go BLAM!!!! Their edges can cut the daylights out of you,too. Very messy,abraded cuts. I prefer the Wilton because it encloses the belt,except where it has to be exposed. Haven't been cut by a belt yet,but have had some blow up on me.

Black_Moons
08-26-2011, 07:18 PM
The rounding effect on a machine like the Wilton Square Wheel grinder,where you can get the belt pretty tight,is minimal,but still there. You can only get the belts so tight,or their seams will tear loose. Those belts are violent when they go BLAM!!!! Their edges can cut the daylights out of you,too. Very messy,abraded cuts. I prefer the Wilton because it encloses the belt,except where it has to be exposed. Haven't been cut by a belt yet,but have had some blow up on me.

I wonder if you could get rid of the rounding effect by just having a platen behind the belt with a huge radius on it to compensate and give a tiny bit of hollow ground.

lakeside53
08-26-2011, 09:37 PM
I'm not seeing that rounding... maybe it's a matter of degree or belt dependant. . My platten is "glass" and I spent a lot of time making sure the 3 inch platten wheels and platten were perfectly aligned.

gwilson
08-26-2011, 10:26 PM
it is a SLIGHT amount of rounding just at the TOP edge of what you are grinding. Might not show up as much unless you are using a finer grit belt,but it is there.

spkrman15
08-26-2011, 11:28 PM
Nice work.

boslab
08-27-2011, 05:56 AM
i know what you mean, we have a 'waterfall' grinder for samples in the lab' the belt is 10" wide and you can see the wave forming in front of the sample, we had norton [saint gobain] in to sort it but apparently it can be reduced with cooling [water cooled platten/belt support?] or air jet on the belt above the sample because they reckon that heat plays a part and belts do get hot as does the support. they seem to be of the opinion that as the belt gets cooked its more prone to the standing wave fault, and when the wave gets too big the sample/work will dig in ripping the belt.
cooling could help?
any thoughts
BTW a nice grinder/linisher, how about a lever/cam at the top to take belt tension off for belt changeing? i have to make one myself so i think i may well be stealing some ideas!
all the best
mark

J S Machine
08-27-2011, 07:48 AM
Looking good. I'm fixing to attempt a blade grinder for making knives. I just picked up a LMS SX2 mill, so all I have to do is get it bolted down, situated, and trammed in. When I do I'll be making chips. Like you, I'll probably have to buy a couple of contact wheels. I think the only way I have seen that you can make decent ones is by having a turned Al hub and a radiator hose piece to cover it. Of course you would be limited to smaller wheels, but I need those kind too so they may work for me.

A.K. Boomer
08-27-2011, 10:01 AM
If your working something critical and you don't want a radius on the leading edge then just try mounting a half to one inch piece of UHMW above your work piece if you can - it can take some abuse yet keep the belt from deformation therefore allowing the workpiece to have a ripple free ride;)

bborr01
08-27-2011, 10:06 AM
If your working something critical and you don't want a radius on the leading edge then just try mounting a half to one inch piece of UHMW above your work piece if you can - it can take some abuse yet keep the belt from deformation therefore allowing the workpiece to have a ripple free ride;)

Something critical on a belt sander?

Brian

A.K. Boomer
08-27-2011, 10:11 AM
Good point - how about critical enough to not want a massive radius on the leading edge:p

noah katz
09-14-2011, 06:31 PM
Re the problem with radius at the top of the work - has anyone tried making the wheel above the platen the drive wheel?

Then the belt would have to be in tension at the top of the work.

wierdscience
09-14-2011, 08:33 PM
The radiused edge is common on wood working belt grinders,there are three ways to deal with it that work fairly well.
Problem is caused by air being pulled in under the belt and floating the belt away from the platen a few thou,when you press your workpiece against the platen the belt is actuall contacting the top edge of the work at a very slight angle instead of running straight in.

One way to counter this is to perforate the platen so the air can escape.This works good,but it's not always practical.

Another is to mirror polish the platen and run it at a positive setting(holding the belt out past the edge of the drive and idler wheels about 1/32".This method works pretty good.However you will have to resurface the platen more often.

Third way is ti fiddle with the table angle setting.Setting the table at 91*instead of 90* will help cancel out some of the efect.

BobL
09-14-2011, 09:06 PM
Or my tensioning system just can't get things tight enough?

Or I'm expecting too much from a belt grinder. :)

What side (before or after the object being sanded) is your primary tensioning?

A primary tensioner on the belt just before the object should reduce this effect.