I think I have a new favourite. <3 thanks guys.
Disc and Belt Sander
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Oh hi there @woodtechs . That looks familiar. 
I’ve already mentioned this to @joeatkin2, but the centrifugal switch in that thing is gone, so the starter cap is never switched in. You can spin start it manually but that goes against your rules so please don’t do that. 
We did open it up and looked inside—someone had taken a needle file to the switch contacts, so there’s no coming back from that. Furthermore even if the contacts were fine, the switch isn’t staying in the location/position it needs to be inside the motor housing, and I suspect this is the current status of the sander. I think it’s fairly obvious what’s wrong once you look inside.
TL;DR: you’ll need to order a new centrifugal switch. Here’s a link (to a link) to the/a manual (different brand but identical), along with some tips on opening the thing up: https://wiki.london.hackspace.org.uk/view/Equipment/Axminster_Belt_%26_Disc_Sander
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Cool thanks for the info!
This thing huh…
https://www.mmtoolparts.com/jet-centrifugal-switch-jsg-6dc-990019
Can someone take a look see inside the machine? Thanks!!
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That link stopped working… try this one:
https://www.ereplacementparts.com/centrifugal-switch-p-939903.html
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Ok I’m not an expert but I’ve done basic google search and looked at the magnetic switch. I assume the first thing is to change the switch contact (we have a spare one in the space but maybe it belongs to @joeatkin2 or someone else). We can then test the motor without the belt paper that I’ve removed (less torque required). If it works changing or cleaning the centrifugal switch is the next step. @liyang did you already access the motor to clean the centrifugal switch? Thank you
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There was no mention of a magnetic switch previously! (Did you mean the on/off & e-stop?)
Yes I (together with two others) figured out how to access the centrifugal switch, and have cleaned the contacts as best as we could around July. But it’s equally (or more) likely that it’s just currently dislodged, and not functioning. See my above link to the LHS wiki for some details.
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Yes.
I’m certain that part is working perfectly fine. The caps also measured fine on our LCR meter.
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Amazing i incorrectly thought you mentioned and issue with the start/stop switch too… no point in me guessing if you have have already opened and cleaned the centrifugal switch.
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It’s on my list of things to fix but until I’ve got the belt sander running I’m not going to take it to bits I don’t like having two machines in pieces at once I think it’s the centrifugal switch that fails but I’m going to have to take the motor bits to figure out what the problem is
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So yesterday @joeatkin2 and me disassembled the thing. Its tool page cannot be edited like other wiki posts there for some reason, so I’ll leave instructions here alongside findings.
Instructions
Here’s a wiring diagram:
Multimeter test points available:
1, 2, 3, 4 - on the power switch
5, 6 - on the starting capacitor connector
7, 8 - on the running capacitor connector
9, 10 - on the centrifugal switch (inside motor housing after disassembly)
In order to access the centrifugal switch:
- Tooling: bolt heads are 10mm, allen key holes are 10mm except motor shaft, screws can be undone with flat screwdriver
- Centrifugal switch as well as winding wires are located inside the motor housing on the right side of the unit - next to disk sander.
- Start with removing the disk part. The disk is connected to the motor shaft with three small hex head set screws (one is missing) which could be accessed through the single hole from the top one by one when the shaft is rotated.
- Remove the casing on the belt end. It is impossible to remove the lower belt drum without removing the motor shaft, so only undo the nut on it.
- Unscrew motor and belt assembly from the stand.
- Remove four bolts on the right side of the motor only. Pay attention to three scratch marks made by someone on the paint of the right cap which are used for alignment when assembling.
- Use a wooden mallet on the shaft (belt drum side) and wooden wedges to move the shaft and undo the right cap of the motor gaining access to the centrifugal switch. Be careful not to damage the wiring, you cannot undo the cap without disconnecting the switch first.
What the final result looks like.
Findings
The problem is, as was mentioned earlier, the centrifugal switch should be normally closed when the motor case is closed and now it is not. As seen on the picture below, It consists of two separate parts - centrifuge and switch. When the centrifuge rotates, its black plastic cap should stop pressing switch contacts, disconnecting the start capacitor and start winding. Currently, black plastic cap doesn’t reach the switch in any position/state leaving it permanently disconnected. Switch is working fine when pressed, wiring is ok, so it is safe to assume it is bad positioning of the centrifuge relative to the switch. And that’s when things stop making sense.
The current distance separating the centrifuge and the switch on a shaft is around 22mm. The shaft is stepped, so the switch cannot move at all in its final position. Switch/bearing step diameter on the shaft is 30mm. We didn’t undo the centrifuge so we don’t know if the shaft beneath it has another step, but visually it seems likely. Centrifuge is also bound to the shaft by the set screw. Here’s how it looks like:
So now we have two possibilities.
- Centrifuge is positioned only by the set screw with no kind of recess or shaft step (or screw moved out of recess) which allows it to slide along the shaft.
Pro: easy explanation. Can be fixed by threadlocker and drilling a recess for the set screw.
Con: seems to be a really bad case of engineering, where looking at the other parts it is unlikely. - Centrifuge is now positioned properly using a step. The assembly is missing some sliding part between it and the switch.
Pro: Redeems engineering.
Con: Spare parts linked above don’t have anything like that.
Current status
@joeatkin2 proposed to contact Jet and ask for a motor exploded view which is missing from the manual.
Sander is partially reassembled. Need to decide further actions.
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Thanks @scythian and @joeatkin2 for the diagnosis!
As we know it has been apart before, it is very possible that it was just not put back together properly.
From some research it looks like the set screw indeed keeps the position of the switch and it needs to be properly adjusted to work… from another vendor, but very similar setup:
I would have to take a look, but as it is adjustable I would guess it is by design that it has no recess or step to hold the set screw. So I think it is possibility 1 not 2. Does the set screw not hold it? Is the whole assembly rotated in the wrong orientation?
This video may help as well, seems that screw is what holds it to the shaft… obviously loctite may help if it is loosening for some reason:
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Let me contact the manufacturer and get the proper clearances and setup.
Trying to avoid guesstimating and stuff
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Go for it… thx
So five months after this is fixed.
Centrifuge is positioned inside using a 6mm thick custom washer and is threadlocked so it shouldn’t slide anymore. Switch part was broken in the process and redone on CNC from tufnol whale. Contacts on the switch are in questionable state.
Previous disassembly instruction should be updated - there’s no necessity to remove belt part and motor from the stand. Remove disk side (cap, two grub screws on the shaft, guard), undo disk side motor bolts, tap belt drum shaft nut with wooden mallet - motor lid on disk side will undo, detach it further using two screwdrivers as levers.
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Thanks Roman it works really well! It would only need a side extraction, i think next to the belt sander (judging by this evening test)
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Awesome! Thanks Roman!!!
Nicely done! Incredible persistence!
