Speed Control Issue

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SteveMaryland
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Speed Control Issue

Post by SteveMaryland »

I have researched this issue and found this thread viewtopic.php?t=29211&hilit=speed+control

I am getting a similar drift problem but my question relates to the setscrew connection between the Speed Control Handle (84) and the Worm Control Shaft (87). See attached photos.

My Speed Control Handle wants to come off the shaft during operation. Pinion teeth are not worn. and the setscrew threads are OK.

But look at that huge oval indent on the Worm Control Shaft! Does anybody know if that still how they come from the factory? Or is that wear from the setscrew?

It's like the setscrew manages to vibrate its way past that sloppy oval detent. I have tightened that little setscrew to the max, but the dial still wants to slip out of engagement with the Idler gear (93) and off the shaft.

Dial Spring (83) does spring-load the dial to prevent drift, but in doing so its force also tends to cock the dial and push it partially off the shaft! And when that happens we lose our gear engagement and our speed control.

Anyway, I have resorted to duct-taping the dial so speed will not drift, but I know that is just a band-aid. I would buy new parts but I really don't see any wear on the current parts unless it's on that shaft. Just not a terrific design to begin with.

Anyone have advice? Didn't Bill Mayo do a mod on the speed dial teeth to address this issue?
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Last edited by SteveMaryland on Wed Nov 15, 2023 3:11 pm, edited 1 time in total.
Mark V, Model 555510, Serial No. 102689, purchased November 1989. Upgraded to 520
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JPG
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Re: Speed Control Issue

Post by JPG »

What shape is the end of the set screw?
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Goldie(Bought New SN 377425)/4" jointer/6" beltsander/12" planer/stripsander/bandsaw/powerstation /Scroll saw/Jig saw /Craftsman 10" ras/Craftsman 6" thicknessplaner/ Dayton10"tablesaw(restoredfromneighborstrashpile)/ Mark VII restoration in 'progress'/ 10
E[/size](SN E3779) restoration in progress, a 510 on the back burner and a growing pile of items to be eventually returned to useful life. - aka Red Grange
DLB
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Re: Speed Control Issue

Post by DLB »

SteveMaryland wrote: Mon Jun 06, 2022 6:35 pm ...
But look at that huge oval indent on the Worm Control Shaft! Does anybody know if that still how they come from the factory? Or is that wear from the setscrew?

It's like the setscrew manages to vibrate its way past that sloppy oval detent. I have tightened that little setscrew to the max, but the dial still wants to slip out of engagement with the Idler gear (93) and off the shaft.

Dial Spring (83) does spring-load the dial to prevent drift, but in doing so it also tends to cock the dial and push it partially off the shaft! And when that happens we lose our gear engagement and our speed control.
...
Anyone have advice? Didn't Bill Mayo do a mod on the speed dial teeth to address this issue?
The indent on my worm gear shaft appears to be oval but is round. Yours looks different in your pic to me. Mine only appears to be oval because of how it is cut into a round shaft. If I remove the setscrew from the handle and hold it in the indent, the indent is clearly round at the depth that the setscrew engages. If I install the handle without the dial it is straight and tight, exhibits no movement relative to the shaft.

For speed drift make sure you have the other spring item 73. I think of it as the detent spring, but I think it engages the back of the dial throughout rotation and provides some small resistance to turning. I've never seen a speed drift problem, just trying to think of things that contribute to resistance to turning. Vibration could be a factor in the control turning.(?) Holding a spare speed control in my hand, I cannot make the worm gear shaft turn by applying pressure to the pork chop in either direction. (JPG mentioned this characteristic in another thread.)

I don't recall a Bill Mayo control handle gear improvement. There is a gear improvement available via eBay. The seller machines out the current gear and replaces it with a steel gear. As far as I can tell this provides an alternative to replacing the handle due to wear of the gear. (Also replaces the bore that fits the worm gear shaft, I would think.) I'd be likely to try this if I was replacing a handle.

- David
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SteveMaryland
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Re: Speed Control Issue

Post by SteveMaryland »

I think my item 73 is in place but have to check. Problem with the item 83 leaf spring is that it bears only on one side of the dial and this tends to work the dial off if there is any slop in the bore or the setscrew.

Vibration does aggravate the drift problem and loosens the setscrew. The setscrew cannot get a good bite on the shaft due to that crazy spherical indent on the shaft. Why SS cut it that way is a mystery.

I will look for that Ebay fix that you mentioned. Aluminum is a lousy material for a small pinion gear like this one. What I would like to do next is just cross-drill a hole in the worm gear shaft and then use a dog-point setscrew - the dog-point will engage the hole like a pin and provide a truly positive hold. come to think of it, a dog point might work better at the quill spring housing - I have had that setscrew slip there as well.

Just try to find a dog-point setscrew at the big box - gotta go to McMaster for it.
Mark V, Model 555510, Serial No. 102689, purchased November 1989. Upgraded to 520
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JPG
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Re: Speed Control Issue

Post by JPG »

If the set screw does not bottom out onto anything, the knob will be floating on the shaft. You will be relying on thread 'shoulder'.

If I were replacing the set screw, I would try a serrated cup point.
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Goldie(Bought New SN 377425)/4" jointer/6" beltsander/12" planer/stripsander/bandsaw/powerstation /Scroll saw/Jig saw /Craftsman 10" ras/Craftsman 6" thicknessplaner/ Dayton10"tablesaw(restoredfromneighborstrashpile)/ Mark VII restoration in 'progress'/ 10
E[/size](SN E3779) restoration in progress, a 510 on the back burner and a growing pile of items to be eventually returned to useful life. - aka Red Grange
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SteveMaryland
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Re: Speed Control Issue

Post by SteveMaryland »

Continuing this thread, I have implemented some mods to my Mark V headstock speed dial which I think may be beneficial.

Shopsmith Mark V speed dial drift occurs at higher speeds. This speed drift is undesirable and unsafe. This drift problem is further aggravated by vibration, which usually accompanies higher speeds. Vibration lowers the drag friction.

These mods are somewhat complex, mainly because of component disassembly and some precise machining required.

Drag friction alone normally holds the Mark V speed dial from drift during headstock operation. If no friction, the Mark V drive would be back-driven toward highest speed (by force of item 116 motor spring) . Drag friction is currently provided by item 83 (dial spring), a leaf spring which bears on the back side of speed dial 84 (when dial is correctly installed, it should preload the spring). This spring loading tends to thrust dial 84 off its mounting shaft, and since the spring is mounted off-center to the dial axis, its force tends to cock the dial. With enough headstock usage, both of these loads eventually defeat the current setscrew and work the dial off the shaft.

Currently the speed dial is retained with a 10-24 x 1/4" long flat-point setscrew which seats in a spherical indent on item 87 (worm control shaft). In my experience, this setscrew and shaft are prone to loosening during usage and do not provide a reliable retention of the dial.

To remedy the speed drift problem, I added a second item 83 dial spring, and I located these two dial springs opposite each other (see picture). This second dial spring doubles the thrust loading and dial drag friction, while the two opposite locations balance the thrust load on the dial axis, thus (possibly) solving both the speed-drift problem and the off-center thrust loading on the dial.
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But while this mod doubles the speed-stabilizing frictional drag on the dial, and also balances that loading, it also doubles the thrust loading on the dial, making an improved dial retention necessary.

A dog-point setscrew provides improved dial retention. To accommodate the new dog-point setscrew, I crossdrilled item 87 (worm control shaft). I want the dog-point to pilot directly into this new crossdrilled bore. Crossdrill location is critical to get this and also get full mesh of the gear teeth between speed dial and item 93 (pinion gear). I found the proper location to be 1/4" from the retaining ring groove on item 87 shaft (see picture).
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The reason the gear face of item 84 (dial) may need to be sanded down is to remedy any interference between that gear face and the face of item 92 (retainer ring), which may happen depending on exact crossdrill location. To be effective, a dog-point setscrew must pilot exactly into a bore, and depending on the exact bore location, some sanding of the dial gear face may be necessary to get a clearance between that face and the retaining ring.
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I have implemented these mods on my Mark V headstock, and improvements in speed-holding and dial retention have been observed.
Mark V, Model 555510, Serial No. 102689, purchased November 1989. Upgraded to 520
DLB
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Re: Speed Control Issue

Post by DLB »

Great write-up and documentation of your modification Steve. Reviewing the thread you referenced, the OP said his would drift at speeds of "M" and higher. Notionally 2400 RPM and up, making a few assumptions. If he resolved the problem he didn't say so or tell us how. I'm wondering if your pre-mod drift started this low? I've seen drift, but only at much higher speeds near the top end.

I especially like the idea of balancing the force of the leaf spring.

- David
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