Belt sander platen is crowned. Normal or no?

[paulrussell]

Hello,

My belt sander is getting a major overhaul. The platen is kinda rough looking (worn unevenly at both ends) but is smooth enough for a belt. I might replace it anyway, but I suspect that is more cosmetic than anything.



What has me wondering is that from front to back the platen is crowned in the center. If I lay a straight edge lengthwise on the mounting bosses and down flush at one end, it floats above the opposite end boss. On the right, by about 3/64, on the left, just over 1/64th. This discrepancy alone makes me wonder.

My platen has six spacer washers that elevate it from the bosses. I used my micrometer and they are all .125" +/- about .001", thus maintaining the curve.

I'm not sure if the center boss is high, an end boss low, or if this is correct.

Should the platen be flat, or is the crown normal?

[algale]

I do not believe this is normal for the platten.

[wa2crk]

Paul.
The platen is curved down at the upper and lower end to prevent the sandpaper from catching but I would suspect the the platen should be flat across it's face. I never checked for that condition but I will try to get to it. You may want to try to loosen the tie bolts that hold the castings together and just wiggle the thing a bit and see if it straightens out when you tighten the tie bolts. I suspect a drop or incorrect assembly. If you take it apart be advised that putting it back together is like taking an octopus for a walk. You never know which way it is going to go!
Bill V

[billmayo]

Hello,

My belt sander is getting a major overhaul. The platen is kinda rough looking (worn unevenly at both ends) but is smooth enough for a belt. I might replace it anyway, but I suspect that is more cosmetic than anything.



What has me wondering is that from front to back the platen is crowned in the center. If I lay a straight edge lengthwise on the mounting bosses and down flush at one end, it floats above the opposite end boss. On the right, by about 3/32, on the left, just over 1/64th. This discrepancy alone makes me wonder.

My platen has six spacer washers that elevate it from the bosses. I used my micrometer and they are all .125" +/- about .001", thus maintaining the curve.

I'm not sure if the center boss is high, an end boss low, or if this is correct.

Should the platen be flat, or is the crown normal?

I just check the backup plate (30), shown in your picture, on both belt sanders I have and this plate is absolute flat both in length and width. I used a machinest rule and a.002" feeler gauge would not fit under the ruler. I cannot find the spacer washers in the parts lists. All belt sanders I have disassemblied have double washers, 12 total, under the backup plate. These washer lift the backup plate above the plane of the drive drum so the sanding belt tracks flat acoss the backup plate. You will notice the wear on the tapered edge of the backup plate in your picture.

The original Shopsmith belt sander had a tapered (belled) surface drive drum, the same as the idler drum. You would over tension the sanding belt while it is moving to break (seat) in the belt. The belt tracking was always somewhat of a problem over time with this original design. Later Shopsmith went to a flat surface drive drum which tracks much better. Only the idler drum kept the tapered surface.

I machine the earlier drive drum surface to a flat surface and install a new drive sleeve (62 - 502932). I install the backup plate with the double washers and using a machinest ruler, check the height of the ruler edge from the drive drum. I find that I needed to reduce this height of the backup plate to be about .020" above the flat surface drive drum to get a longer life from the sanding belt. I use different thickness washers to achieve this height. This is only my solution for a longer sanding belt life and will not be found else where. I am sure Shopsmith does not approve of this change and adjustment.

[JPG]

I do not believe this is normal for the platten.

I do not think this is normal for the bosses.

[paulrussell]

Well, I've got the belt sander torn down and did the cleanup/lube per the sawdust session. However I believe along with the platen bosses being out a bit, I have a bigger issue. My drive drum bearings seem tight. There isn't any play or wobble, but disconnected from everything there is no "spin" to them. They feel like the lube inside is gummed up.

Unfortunately, Shopsmith appears to only sell the entire drive assembly, and not the bearings separately. Does anyone know a good source for replacement bearings?

Also, I note I have the crowned drive drum. Nick talks about turning the drum and replacing the rubber with new. I've not a clue how to go about this. Take it to a machine shop or ??

Or should I just bite the bullet and buy a new assembly?

[JPG]

Well, I've got the belt sander torn down and did the cleanup/lube per the sawdust session. However I believe along with the platen bosses being out a bit, I have a bigger issue. My drive drum bearings seem tight. There isn't any play or wobble, but disconnected from everything there is no "spin" to them. They feel like the lube inside is gummed up.

Unfortunately, Shopsmith appears to only sell the entire drive assembly, and not the bearings separately. Does anyone know a good source for replacement bearings?

Also, I note I have the crowned drive drum. Nick talks about turning the drum and replacing the rubber with new. I've not a clue how to go about this. Take it to a machine shop or ??

Or should I just bite the bullet and buy a new assembly?

Only 'dry' bearings 'spin'. Properly lubricated ones(grease) are 'sluggish'.

[paulrussell]

Only 'dry' bearings 'spin'. Properly lubricated ones(grease) are 'sluggish'.

Bad word selection on my part. Indeed bearings should not spin. The drum does not spin -- In the Sawdust Session video Nick demonstrates a bit of spin on the drive drum as being proper. The bearings are more than sluggish. Turning the drum spindle with no sanding belt and disconnected from the SS meets with more than acceptable resistance.

Given that I believe the grease in the bearings has turned to mud anyway, I carefully pried off the seals. I added a small amount of white lithium grease to both bearings, and worked it in. The assembly now behaves like I would have expected. I'm not sure if I should flush the bearings of the old grease and completely repack, or go with my fix as is.

[JPG]

Bad word selection on my part. Indeed bearings should not spin. The drum does not spin -- In the Sawdust Session video Nick demonstrates a bit of spin on the drive drum as being proper. The bearings are more than sluggish. Turning the drum spindle with no sanding belt and disconnected from the SS meets with more than acceptable resistance.

Given that I believe the grease in the bearings has turned to mud anyway, I carefully pried off the seals. I added a small amount of white lithium grease to both bearings, and worked it in. The assembly now behaves like I would have expected. I'm not sure if I should flush the bearings of the old grease and completely repack, or go with my fix as is.

Do not knock 'success'. Repetitive prying of the shields will lead to failure of the shields to 'stay put'.

That said, they be quite easy to replace(the hard part is getting to them, and 'you are there').

VXB will have you new bearings by the week end.

[robinson46176]

If you add lube to bearings and then order new bearings to have in case yours fail yours will last "forever"...


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