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G8688 Lathe - Adjusting Cross Slide Tension

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PHPaul

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#1
I was making an adapter on my lathe and needed to do a bit of boring. Even with very light cuts, the compound was moving up and down noticeably.

I managed to finish the job and when I was cleaning up the lathe I found an Allen screw laying in the tray. "Hmmmm," sez I, "Coincidence? I think not!"

So some investigation revealed that it came from the retainer plate on the front of the cross slide, behind the carriage. I call it a retainer plate as there isn't a gib in the normal sense.

Wound up taking the entire cross slide and carriage assembly off the lathe so I could get at things to replace the errant screw. All three screws were loose and flopping around.

The retainer plate is held in place with three Allen screws with set-screw and lock nut adjusters between them: X o X o X with the X's being Allen screws and the o's being adjusters.

I assume (yeah, I know...) that the idea is to use the adjusters to set the gap between the retainer plate and the way and then snug the Allen screws to lock everything in place. My problem is I can't snug the Allen screws enough to give me any confidence they'll stay snug. So, two questions:

1. Am I just not fiddling with the adjustment enough and if I get that right I should be able to snug the screws up in good shape?

2. Or, should I clean things up good and use loctite on the screws?
 

markba633csi

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#2
Can you post a picture? I've looked at the 8688 and it looks like it has conventional gibs and adjusting screws- I don't see the retainer plate you mentioned unless they've changed the design?
You shouldn't need loctite as far as I can tell..
mark
ps AH I think I understand now- you mean the back of the cross slide, behind the carriage. Yes there's a plate with adjusters. Some lathes use shims, yours apparently uses screws. Snug it as tight as possible while still permitting free travel of the carriage. Loctite is fine there, I would use the removable kind 242, in case you have to remove it
I believe you tighten the allen screws first, then the adjusters. I wouldn't use loctite on the adjusters, just the allens
 
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royesses

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#3
I used to use loctite on my 7x10. I made tapered gibs for it and now use an adjustment screw to adjust the gibs. Use blue loctite.

Roy
 

PHPaul

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#4
No pictures handy, and I would have to disassemble the cross slide and carriage to get one, but yes, the front adjustment is the same as the back: A plate with setscrews.
 

PHPaul

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#5
Thanks, Roy. I'll do that next time I get a little shop time.

Navy vet here (22 years) what branch were you?
 

royesses

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#6
Thanks, Roy. I'll do that next time I get a little shop time.

Navy vet here (22 years) what branch were you?
Army, I did 3 years 1968-1971 16 months in Berlin and 12 in RVN. Thank you for your many years of service.

Roy
 

homebrewed

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#7
The G8688 doesn't use gibs for the carriage. I own a 7x12 too so I know it well. The stock slide plates are a PITA to adjust -- one set of screws is used to push the plate out, the other pull it in. I replaced them with molybdenum disulfide-filled nylon plates and shimmed to get a sliding fit. And just one set of screws, to attach the plates to the carriage. The new front plate will need a relief machined into it to accommodate the apron pinion gear.

For more information on this mod, check out the files section on groups.io/g/7x12MiniLathe. To give proper credit where credit is due, another member of hobby-machinist.com (old toolmaker) came up with this particular design, not me.

This approach is simpler than the tapered gib mod. It has worked well for me so far. I was motivated to implement the mod because my carriage also was tipping when I attempted parting operations.

You also want to make sure the compound gib screws are pretty snug -- the forces during parting will try to rotate the compound. Parting on these little lathes probably is one of the more demanding things you can ask them to do, revealing any shortcomings in fit and adjustment.
 

markba633csi

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#8
Sounds like a less than desirable design for the slide plates (and I'm being kind) I would redo it all and make it like the Atlas, with shims
If I owned one
mark
 

PHPaul

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#9
Homebrewed, thanks for that link, I'll check it out. Sounds like just the ticket.
 

homebrewed

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#10
Glad to help. BTW I got my MDS-filled nylon from McMaster-Carr. You don't HAVE to use that, though. Folks have used brass and even acetal/Derlin with good results. The slide plates are so big that the load is spread out a lot.
 
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