2 X 48 Belt Grinder (again)

I think I'm going to go to 1/4" steel on the vertical support.
Robert
 
you get a nice looking motor, and a nice piece of I beam at least. Oops. you would have to spend a lot of time cleaning the I beam up.
 
I have found one monor issue that maybe someone can help me with. When the belt is at speed I can easily align the tracking to be perfectly centered on the platten. When I turn the grinder off and the machine slows the belt move over to the right slightly. Only 1-2 mm but it could contact the table cutout. Anyone have any insight as to why tracking would change with speed?
Robert
Click to expand...

Robert,
As I have been doing some improvements on my belt sander this last week, I think I have the answer to this problem. When I had my tracking adjusted just right there was a slight difference in position as you said. Although it wasn't hurting anything, it bothered me. I think you have more belt tension than I do, but I found the belt tension was deflecting the upright frame about an 1/8" at the top. My frame upright is 1/4" thick aluminum and 6" wide at the bottom and 4" wide at the top. I never thought it would move that much. When I put the new motor on ( which like yours is 3450 rpm .... It was what was on hand) I noticed this deflection. I put a gusset on the bottom of the frame ( see new photos in my build) and the problem is gone. The tracking stays perfect at all speeds because that deflection is gone. If I was to make another machine, I would make the frame from 3/8" thick aluminum or better yet steel , as it would deflect less I think. I would still put the gusset in also.
 
Thank's Mark. My vertical arm has a built in "gusset" at the base but the arm is probably too thin. I plan to replace it with 3/16" stainless to reduce deflection. I will report back when I get the material and make this modification.
R
 
I installed the new vertical support. It is 3/16 angle and very rigid.

29116384712_0c97a6f395_b.jpg

Unfortunately, the tracking still changes slightly when it is running. The belt moves to the right about 1-2 mm. Not a big deal but I am not sure why this is happening. I would not expect the running belt to put any net force on the upper arm? Should I crown the bottom pulley?
Robert
 
rwm said:
I installed the new vertical support. It is 3/16 angle and very rigid.

29116384712_0c97a6f395_b.jpg

Unfortunately, the tracking still changes slightly when it is running. The belt moves to the right about 1-2 mm. Not a big deal but I am not sure why this is happening. I would not expect the running belt to put any net force on the upper arm? Should I crown the bottom pulley?
Robert
Click to expand...

Robert,
It may help to crown the bottom pulley. I put a 1 1/2 to 2 degree crown on my bottom pulley. I looked at a lot of belt sanders before I built mine and they all had a slight crown on the bottom pulley. The top pulley is straight, with no crown. I'm not positive that will help but it is how I found most to be made. Mine does not move at all.

Edit: in your photo it appears neither pulley is crowned. If this is correct, you need a crown on the bottom pulley to keep the tracking consistent. ONE pulley must be crowned slightly to hold the tracking.
 
Mark-the top pulley is crowned about 1.5 deg on each side. Hard to see.
I loosened the pivot bolt for the upper arm slightly and this seems to have fixed the problem somehow. It doesn't make sense since it now theoretically has a little more slop. Anyway, it tracks true!
Robert
 
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