Broken Power Coupler

[jimsteinmetz]

First time use of a used (new to me) band saw on my Mark 7 produced some interesting results. I had a 1/2 inch blade installed and all adjustments made. FYI-this is not the first time I've used a Shopsmith band saw as I had one with my 520.

I was going to cut a U shape into a 2 inch thick piece of oak. Cutting down one side (2 inches in length) I noticed some noise and vibration but it seemed as long as I cut slowly it was OK. I then cut the opposite side and noticed the same effect. After completing the second cut I didn't see anything wrong so I started to make a long diagonal cut to start cutting out the middle. About an inch into the cut the band saw started shaking and the blade stopped. Pretty easy to see why the blade stopped as the coupler was now in two pieces.

Today I looked closely at the saw trying to figure out what was wrong and how this happened. I found a few things wrong with whoever used this saw last. But I'm not sure if these issues were the cause or if they contributed to my problem. The first issue was with the adjustment of the upper guide block. You could adjust the blocks out but not in. I found that the adjustment knob was not installed correctly so I fixed that.

I then noticed that the blade guard didn't look right. I found that the bolt that holds the upper roller bearing was in the wrong place. The location was swapped with the bolt placement for the bolt that holds on the blade guard. So the bearing was too high. That has been corrected.

Also I noticed that there is about 1/32" top to bottom and side to side play in the upper wheel. I'm not sure if that is normal or not.

I then noticed that with the band saw installed and tightened down, there is play in the band saw. I measured at the drive hub, and with pressure applied to the band saw table, I could move the drive hub up and down about 1/16". I removed the band saw and installed the extension table in its place and there was no play with the extension table. So I am suspicious that this problem is with the alignment of the band saw mounting tubes.

Fortunately I have a spare power coupler. But before I order a replacement (new spare) or go any farther I thought I would ask for comments and ideas from the group.

Thanks.

Jim

[charlese]

Hi, Jim!
Does your Mark 7 have a Powwer Pro headstock?

When I was having problems with the PP and the bandsaw, I called SS and sent them the broken coupler(s) They sent me replacement couplers.

[garys]

I think your suspicions are correct about the band saw moving 1/16" could be the cause of the broken coupler. Movement like that will put side to side motion on the coupler and it can crack. Once a crack forms, it gets worse fast and will break.
I would find out why the band saw isn't sitting tight on the Shopsmith. If you solve that, you should have the problem taken care of.
Over the years, I have broken 2 couplers. I feel that this is why Shopsmith made them from plastic. They act as a safety much like a shear bolt on a shaft. If the coupler breaks when something goes wrong, it prevents more damage to more expensive parts.

[dusty]

First time use of a used (new to me) band saw on my Mark 7 produced some interesting results. I had a 1/2 inch blade installed and all adjustments made. FYI-this is not the first time I've used a Shopsmith band saw as I had one with my 520.

I was going to cut a U shape into a 2 inch thick piece of oak. Cutting down one side (2 inches in length) I noticed some noise and vibration but it seemed as long as I cut slowly it was OK. I then cut the opposite side and noticed the same effect. After completing the second cut I didn't see anything wrong so I started to make a long diagonal cut to start cutting out the middle. About an inch into the cut the band saw started shaking and the blade stopped. Pretty easy to see why the blade stopped as the coupler was now in two pieces.

Today I looked closely at the saw trying to figure out what was wrong and how this happened. I found a few things wrong with whoever used this saw last. But I'm not sure if these issues were the cause or if they contributed to my problem. The first issue was with the adjustment of the upper guide block. You could adjust the blocks out but not in. I found that the adjustment knob was not installed correctly so I fixed that.

I then noticed that the blade guard didn't look right. I found that the bolt that holds the upper roller bearing was in the wrong place. The location was swapped with the bolt placement for the bolt that holds on the blade guard. So the bearing was too high. That has been corrected.

Also I noticed that there is about 1/32" top to bottom and side to side play in the upper wheel. I'm not sure if that is normal or not.

I then noticed that with the band saw installed and tightened down, there is play in the band saw. I measured at the drive hub, and with pressure applied to the band saw table, I could move the drive hub up and down about 1/16". I removed the band saw and installed the extension table in its place and there was no play with the extension table. So I am suspicious that this problem is with the alignment of the band saw mounting tubes.

Fortunately I have a spare power coupler. But before I order a replacement (new spare) or go any farther I thought I would ask for comments and ideas from the group.

Thanks.

Jim

Since the extension table is solid when locked, I would check the band saw tubes without the band saw to determine if they are solid. I am betting that they are. Now, if you have a problem at all, it is within the band saw. However, I do not believe that a movement as small as you describe (1/16" measured at the hub) is a problem.

[jimsteinmetz]

Sorry for the delay in responding. Our house is up for sale and we usually have "lookers" on Thursday-Sunday. So everything has to be nice, neat and put away. Monday and Tuesday are our catch-up days and Wednesday is usually the day I have to play. Then I clean up and wait for next Wednesday.

Thanks for all the responses. Charlese, yes it is the Power Pro headstock. A few things I have read on-line talk about issues with the headstock and bandsaw.

Garys, I agree and understand the safety involved by breaking. Just like a fuse in an electrical circuit.

And finally Dusty. I have checked the band saw tubes without the saw attached. The tightness(?) seems to vary a little depending which tube is on the left and which one is on the right. In other words installed one way and the a a bit loose (very little) and reverse them and they are tighter.

So I have installed them in the tighter location. After attaching the saw to the tubes I still have the play at the drive hub and I can see movement in the tubes in the accessory mount. However, with the coupler installed it appears that it can "absorb"(?) this small amount of movement.

Also today I have installed the Carter Products upgrade kit and a new blade. Things seem to be working much better.

I am now checking the rest of the alignment. The only issue that I can see is the upper blade guide column seems to have a bit of side to side play. The manual mentions adjusting the nylon bolt to remove the play. I found that the bolt was loose. Finger tightening it resolved the side to side issue but if I snugged it up a bit with a wrench the blade guard had difficulty moving up and down. I'm a bit concerned about leaving this finger tight. Any suggestions on this?

Again thanks to everyone for their advice and suggestions.

Jim

[billmayo]

I put a nut on the nylon screw, and play with locking the nut, not too hard and test the side movement. I takes me a few tries to be happy with this adjustment.

[JPG]

. . . The tightness(?) seems to vary a little depending which tube is on the left and which one is on the right. In other words installed one way and the a a bit loose (very little) and reverse them and they are tighter.

. . .

Jim

When the clamp is tightened to both tubes, is there clearance(equal) at BOTH ends of the clamp(the knurled thingie).

[jimsteinmetz]

Thanks for the replies.

Billmayo--I thought about putting a nut on the nylon bolt and locking it down that way. Wasn't sure if it was just me having an issue like this. I will give that a try. Simple solution that I like!

JPG--I think what you may be asking is the left and right hand studs in the locking handle adjusted correctly and equal. Yes they are. Sitting here thinking about it I wonder if I could flip the handle 180 degrees and see if things change. Of course that would reverse the direction of loose/tight but would be a simple test. Although the extension table seems tight.

Perhaps this play is normal? Or near normal? I'm getting ready to place an order for some other replacement parts from Shopsmith which are mainly for cosmetic repair. I thought about replacing the eccentric mounting tubes to see if that helped but they are about $18 each. Don't know if I want to try a replacement at that price if this really isn't an issue.

Jim

[dusty]

Don't discard your broken coupler; it can be used as a tachometer accessory. I have attached the reflective tape to one of my broken couplers. When I want to check headstock speed, I just attach the coupler. Could not be easier (except with a built in tach).

[richardrouse]

This is a bit off topic, but sort of related.

I just bought a used Mark V and am excited to get it up and running. Unfortunately, I can't seem to locate the shaft coupler, and while I found the correct item on the ss website.. the tinkerer within is wondering why I can't just use a jaw coupling, or some other flexible coupling.

Thoughts?