Logan 820 Shifter Rack Issue

T

tmenyc

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The Logan 820s are set up to control the back gear by a knob on the front of the headstock. The knob is attached to a shifter rack which "engages a pinion which rotates the eccentric shaft, thereby swinging the back gears into mesh" (quotes from Logan 820 manual). The weakness of the setup is that this critical piece is held in place by a smallish clamping ring, which is held in place by a small set screw. And, of course, I'm guessing it's all meant to be repaired upside down after one loosens the bolts holding the lathe to the bed. If this isn't an example of something being only as strong as its weakest part, I don't know what is...
This is actually the second time I've had the shifter rack come out in my hand; getting it back in the first time must have been beginner's luck. I guess I lost track of the last time I checked the set screw. I get my hand/wrist underneath and inside, turn the eccentric, think I've gotten the gear in the right place, but when I slide the shifter rack back in it doesn't work the gear as it should.
I'd appreciate any assistance on this, if anyone can talk me through doing it right.
Yes -- to preempt the response, I do know it gets special mention on the Logan Lathe board operated by Scott Logan; there is an instruction page for it. But that's pretty cryptic and just says "this part can be difficult".
Also, if anyone has a better idea for clamping it in place I'd love to learn. The drawing from the 820 catalog is below. There is no drawing I know that shows it in place.

Many thanks!
Tim

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I've used a couple of screw drivers to assist and found the shaft is going to rotate as the leaver is inserted. So have it one tooth off when you start, meaning the leaver further out than you think it needs to be. Try a bit of Locktite on the screw when you reassemble.

Ron
 
Just to clarify, it’s the collar (#1 in the figure) that’s coming off? I haven’t had that issue yet, but mine was missing that piece so an early project was remaking it. I used a socket head cap screw in place of #7 because it’s what was lying around, and it feels quite secure. This may be a case where the smaller screw actually worked out better because it’s “springier”. Is the stock one coarse or fine thread?

Reassembly wise, cutting a slot in the end of eccentric shaft makes life much easier. Then you can turn the shaft into position with a screwdriver. It is a real bear otherwise. It is possible to remove the eccentric shaft from the headstock on the machine.
 
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Ron --
Many thanks. I'm not clear how to use the screwdrivers. One to push the back gear, I assume. How do I know when it's "one tooth off"?
Yes, the Loctite is clearly necessary; shouldn't have forgotten it before.
Kyle -- yes, your idea of cutting a slot in the eccentric has been raised before. That would definitely simplify things. The trouble is that my shop is not equipped for that kind of operation, although I've certainly considered doing it. One of these days...
I did replace the tiny set screw with a longer socket head bolt the last time, so it's indeed easier to get at and back in than before.

Thanks,
Tim
 
tmenyc said:
Ron --
Many thanks. I'm not clear how to use the screwdrivers. One to push the back gear, I assume. How do I know when it's "one tooth off"?
Yes, the Loctite is clearly necessary; shouldn't have forgotten it before.
Kyle -- yes, your idea of cutting a slot in the eccentric has been raised before. That would definitely simplify things. The trouble is that my shop is not equipped for that kind of operation, although I've certainly considered doing it. One of these days...
I did replace the tiny set screw with a longer socket head bolt the last time, so it's indeed easier to get at and back in than before.

Thanks,
Tim
Click to expand...
Hi Tim. Yes, I used the screwdriver to spin the back gear. Let's see if this helps. The shifter rack will be about 1-1/2" out of the headstock when it both locks and the eccentric shaft is fully lifted into contact with the spindle shaft.
  • Pull out the bull gear engagement lock so the spindle free spins.
  • Position the shifter rack with its teeth down and pulled out of the headstock to where the latch key pops out.
  • Use the screwdriver to rotate the gear on the eccentric shaft until it contacts the shaft and seats the gears.
  • Release the latch key and push in on the shifter rack until the shifter rack teeth start to engage the gear "and" the eccentric shaft starts to rotate.
  • Disengage your screwdriver but don't let the eccentric drop! The eccentric needs to remain in contact with the spindle shaft and only when the shifter rack is pushed in should the eccentric start to spin out of contact with the spindle shaft.
  • Push the shifter rack all the way in and see if it rotates the eccentric out of contact.
    • Success? Yea!!
    • Not so good? This is where the "one tooth" on the eccentric comes in.
    • With your screwdriver, re-seat the eccentric. Then carefully try to rotate the eccentric by one tooth so it is just that amount out of full contact.
  • Again push the shifter rack all the way in rotating the eccentric and check again to see if the shifter rack rotates the eccentric out of contact with the spindle. I only had to rotate the eccentric by one tooth worth of rotation to get it set.
Make any sense?
 
KyleG said:
FWIW I just used a hacksaw to slot mine, and it came out fairly professional looking.
Click to expand...
I was thinking a hack saw and a jeweler's file if necessary to clean it up. I didn't really have that much trouble, but for once I may have just had some luck.

Funny? Both the Logan's I've owned came to me with the shifter rack adjusted so all the way in was engaged! So at least two previous owners had trouble, obviously not something to think "I'm the only one." And not when Scott said he used to get a couple of calls a week!

R
 
good news! With thanks to @Shiseiji and @ThinWoodsman (who used to be around here), my shifter rack is fixed, and fixed to stay fixed. Ron and I had a great talk last week, of course hours before we went away for a family weekend out of town, and today @ThinWoodsman was in town and came over. Between Ron's method and Thin's agile hands, we got it fixed. I had the method allright but just couldn't manipulate my getting-older hands around the Logan's eccentric enough (underneath the headstock, then twisted up to get at the eccentric) to get the proper grip. He was able to handle it. Then, with the proper point identified on the shifter rack, we put it on my vise and punched, then drilled a proper locator hole for the set screw to fit into so it won't fall out again. Now it's working fine!
Many thanks again, Ron.

Tim
 
Tim, thanks for the feed back, and that the method was helpful. My hands certainly aren't what they used to be! Now I'm wondering if a cord could be passed under the eccentric shaft and used to lift it. Sorry I didn't think of that sooner, maybe it will help someone in the future.

Ron
 
That could work...I do like the idea of pulling the eccentric and cutting a notch for a screwdriver. However, in the realm of the possible for me, getting that set screw down into a landing hole so it won't come out again is a great solution.
Tim
 
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