Jet 10-20 sander malfunction

It has not been the greatest of mornings! Whilst using my Jet 10-20 to thin down a guitar top, on one pass it seemed to spuriously add about 0.5mm to the depth of cut. I had stopped the drum whilst making adjustments to the belt tracking, and on re-starting the cut had dramatically increased. OK, so I imagined I must have somehow moved the handwheel, and since there was plenty of meat left, I carried on and evened up the thickness OK. However after stopping the machine again for final thickness checks and a cuppa, I put the top back through for a final pass without changing any settings.
Well, the top is now wrecked.

This time I was sure I hadn't touched anything, so carefully checked the machine. No play in bearings, abrasive nice & tight on the drum, no bulges where the belt goes into the drum, and finally I ran the height adjustment up & down several times - couldn't find anything wrong ... so ...
I started to thin down another top set to ~4mm before jointing. All going well until I had to adjust the tracking again. Put a top half back through without touching anything else on the machine, only to think "that sounds like a heavy cut ..." It was about 1mm, taking the half down below 3mm, enough to mean I can now only use that set for ukes.

Now I know about the height screw/nut failure problem that is apparently quite common on these machines, but I always imagined it would be a catastrophic event - it would simply fail, and the screw would no longer raise or lower the drum, which would presumably have dropped down in the process.

My drum still winds up and down OK though!

Is it the case that the failure mode is initially intermittent depth of cut increments?

I think I have to assume the worst and contact the good Mr Timms about a replacement.

One more question - does the 16-32 suffer from similar problems or is that a more robust machine? I don't like having to double feed guitar tops at the best of times, so a 16-32 might make some sense if I can find room (and some cash).

I've not heard of the 16/32 suffering from the same problem.

It is very common for all sanders of this type to take more material off each time you take a pass without changing the depth of cut. The conveyor belt on some is rubber and compresses a bit (like mine) or the cantilever system such as on the Jet deflects under pressure. They will continue to take off material without any adjustments for 5 or more passes. Especially with the double pass method you need to use on a guitar size top through the 10/20.

Not saying this is the case here, but it is something to keep in mind.

Thanks Allen. I try and utilise the fact the sander will continue to take material off for several passes when I am approaching final thickness. In this case the top had probably been through two or three times at the same setting, and I was expecting to just tease down that last couple of thou with the final pass. All I can think of is that the reaction from stopping & starting the drum between passes may have prompted the drum assembly to take up a different position on the height adjustment screw. I just pulled the spindle out to send off to Ken, and whilst the screw threads in the aluminium cantilever casting are still intact, they look worn and the spindle wobbles around quite badly. Given I knew these machines may have issues with the screw threads, and that my spindle has the under-sized dimensions Ken reported as potentially problematic, I'm annoyed that I ignored the first warning sign! However I managed to convince myself I must have moved the height adjustment wheel whilst bending over it messing with the belt tracking.

Hoping Ken can effect a repair, but I just spotted that Axminster have the 16-32 on special offer at the moment .....

I've used the Performax 16/32 almost daily for over 10 years without a problem except for having to change the feed belt once (good upgrade BTW). When Ken Timms posted about the screw problem a couple of years ago I went ahead and bought a spare one waiting for mine to go out. I'm still waiting. I think it's a fair bet to say the 16/32 models don't suffer from the same problem as the 10/20s do.

Thanks Chuck. I'm seriously tempted by the 16-32, but it's difficult to justify the cost given I only make a few instruments a year. I only build one model of guitar, however with a 15" lower bout it is an ideal size for the 16-32 sander! Double passing through the 10-20 is usually an issue, and however much time I seem to spend on drum alignment there is frequently a detectable step left in the centre by the drum end. I guess that could be a function of a degenerating spindle though, so probably sensible to see how the 10-20 performs after repair, and make a decision then.

The 16/32 can be finicky with tracking. It has a ceramic guide that goes underneath that fixes it, for the "sandpaper" conveyor belt. I swapped to a rubber belt - forgot where I got it from but I think Chuck referred to it long ago - white with squares, have had it for years.

Unfortunately, the edges are getting worn out because of the sandpaper attachment to the drum, which is exactly the reason why I don't really believe the "32" in the name. Nor the 16, since, IMO, its limited to the sanding area between the attachment points on the ends.

However, it works for me!

Thanks Kekani. I agree with you about the effective drum length being between the attachment points - it is the same on the 10-20 and I can never totally eliminate a bulge in the abrasive at the end nearest the motor. Out of interest, what do you think is the true effective drum width on your machine? It would save me an 80 mile trip to go and check one out first hand! Just looked, and Axminster list a rubber coated conveyor belt as an accessory.

Repair Kit complete Paul ..All you have to do is saw off the offending bit and bolt this on in it's place.
repair kit by Ken Timms, on Flickr

Crikey Ken, how much would a pre-emptive strike against my sander set me back?

Yours truly, and in great admiration
Sven

Hi Sven. I think we both made a similar enquiry when Ken last posted about this issue a few months ago. Because it meant sending the spindle off to Ken and I was using the sander pretty regularly at the time, I didn't follow it up. I have now lost a decent guitar top, a rather nice rosette, a whole days work and reduced another guitar top to ukulele use only ... so .... my advice would be to make your pre-emptive strike while you have the chance!

The parts Ken has made are absolutely first class and fit perfectly - highly recommended.

If your machine has the casing that wraps over the top frame bar (not the earlier "open top" one shown in the parts diagram) then I recommend NOT removing the tilt adjustment screw before removing the casing. Undo the two grub screws to release the bar from the pillars and remove the two cap head screws that secure the casing to the pillars, but leave the tilt adjustor in place. This will prevent the spring from shooting across the workshop

Thanks again Ken

Thanks for the description. I might surprise Ken with a greasy screw, after a couple of beers natch, at Hollesley this year.

Sven

I might surprise Ken with a greasy screw, after a couple of beers natch, at Hollesley this year.

Click to expand...

Ken. I'm not sure exactly what Sven has in mind, and I'm not one to judge other people's life choices, but do be careful.
Miguel

Since English isn't my first language I have no idea what I might have written.

http://www.oxforddictionaries.com/definition/english/screw

See meaning #4.
Just one of the pitfalls in dealing with the English language. I have also made some terrible gaffes when trying to speak Spanish. The only solution is to laugh and move on.
Miguel

Ha ha fanx man but in fact I was completely aware of what could be implied by greasy screw. Just played the innocent Swede card (if you would believe there is something like an innocent Swede).

Just to let you know i'm trying to replace all my pic's that Photobucket kindly removed and I started with this thread first..Let me know if you can see it again on page 1

Timbuck said:

Just to let you know i'm trying to replace all my pic's that Photobucket kindly removed and I started with this thread first..Let me know if you can see it again on page 1

Click to expand...

if you mean the picture of the repair kit you made for Paul, Ken, then yes it's there.

Hi Ken. I might as well take advantage of this threads reappearance to say that I went ahead with the special offer on the 16/32 from Axminster, and in my experience it's a far, far better quality machine than the 10/20. In particular, belt changes are a lot less fiddly (almost a pleasure in fact) and the conveyor tracking I find hardly ever needs adjusting. In fact I can't recall when I last needed to do it. It was a constant battle with the 10/20

The guy who bought my 10/20 wasn't an instrument builder, but knew all about your height screw modification! It was the main reason he decided to buy it.