Removing Flex in 9x19 Compound Slide Base / Gibs

[jayriz]

Hey,

I've been a long time lurker since I've always been able to find what I was looking for with the search and not much to contribute beyond what others already had - but I have a problem I'm looking for some ideas on solving I couldn't really find already addressed.

I have a Grizzly 9x19 and I thought I was on my way to getting this thing dialed in as much as the machine is capable in terms of rigidity and I just found another issue. I already created a new compound clamping ring for it to use the 4 bolt points instead of 2, and that helped a lot. But when pushing on the QCTP I noticed there was about 4 thous of play in either direction. I started looking to see if it was coming from and I could actually see the movement (thanks to the lube moving) occurring, and it is in the compound slide, between the compound slide "lower half" (the fixed section with the gibs and gib adjustment screws) and the "upper half" (the section that slides). Those two halves should obviously not show any separation and just mate tightly together. So I thought maybe the gibs loosened up some, but they were still nice and snug. Just to test I tightened them as much as I could and it had no effect.

I am going to disassemble it to inspect for any issues, but I have a couple parts I need to finish first. Until then, I'm wondering if anyone has any tips on how to resolve this (maybe polishing the mating surfaces?) or what to look for.

Once I get that squared away I can start address another mystery that is occurring where my larger parts are coming out with a very slight taper even though the tailstock is zero'd, part centered to zero, and the TDI reads zero up and down the ways.

Thanks!
-J

 

[ScrapMetal]

As to the taper issue, have you tried leveling the lathe front to back?



-Ron

 

[jayriz]

Thanks for the reply. As it turns out my bench went out of level a bit throwing my lathe level off. I suspect this happened when I was trying to a out of round part that was trying to get bench to walk away. Oddly, all this time I didn't make the connection to the straight part and the levelness of the table because I assumed everything was relative, and even if you stood the thing on it's end at 45 degrees if it was a sufficiently rigid/stable setup it would still cut straight. Learn something all the time...

Anyone have any tips for making the compound slide mate snuggly? I pulled it apart and the gibs were still fine (I rarely slide with the compound) and it wasn't debris or anything. I don't see any apparent reason why if I locked down the gibs tight as drum it wouldn't stop the ability for it to rock (let alone slide anymore, but just for the purpose of seeing if I can get the play out of it).

Thanks,
-J

 

[Tony Wells]

J can we get a picture or two of your lathe? You're quite right. The gibs should get tight enough to lock it down completely. Since they apparently won't, you definitely have some issue. May be minor, or not so much. No doubt fixable though.

 

[12bolts]

Jay,
The movement you refer to, if it is along the sliding axis of the compound then it is going to be wear in the feedscrew and nut and you will need to live with it or make a new screw & nut, (although 4 thou is pretty reasonable for a hobby lathe). If it is across the direction of sliding movement, check the movement at either end of your compound travel. If it is more "apparent" at 1 end or the other then it may be uneven wear. However if it is clean and assembled correctly then you should be able to tighten the gibs sufficiently to lock the compound and stop all movement. Without cranking too hard on the gib screws you should be able to nip them up so that the compound wont slide at all. If you cant then I would be looking for problems with assembly or wear. Are you positive that the gib keys have been orientated correctly?
The compound, or for that matter the cross slide or carriage, are never going to mate together "tightly" as there needs to be clearance for movement to occur.
If you think that the dovetail section is good then maybe the movement is actually occurring in the mounting of the lower fixed half of the compound on to the cross slide but the movement is only apparrently and visible in the dovetail section.

Can we get some pics?

Cheers Phil

 

[Richard King]

J can we get a picture or two of your lathe? You're quite right. The gibs should get tight enough to lock it down completely. Since they apparently won't, you definitely have some issue. May be minor, or not so much. No doubt fixable though.

I have seen the gib set screw hole is not tapped all the way through and when you tighten the setscrew it jams up in hole before it hits the gib. Sometimes they design the set screw to be a dog point which means the end of the screw is smaller and the treads are tuned down about 1/8 from the end and if the hole isn't drill and tapped completely the dog point is smaller and that hits the gib. I'm not sure on a Grizzly, but sometimes on other machines that have that type of gib they counter bore a small hole in the gibs so the set screws will also hold the gib laterally as well as tightening the slide. Maybe someone took it apart and lost the dog points and put in regular ones and that's why it seems to have no affect.

I would suggest you buy longer sets screws and put jam nuts on the outside so you can tighten the gib so it moves in and out with a slight drag (.0005" to .001") clearance. You need the clearance so you get oil in there, to tight will make it gaul up because lack of oil. If there is a screw in the middle of the slide I would leave the lock nut off the one and make that a cross-slide /compound lock. I'm bit cofused as to the parts names your using. The part that slides on the bed ways is the "Saddle" The top side of the saddle ways and the part that slides on them is the "Cross-slide" The slide that holds the tool holder is The Compound.

So you would say Top of saddle cross-slide ways and upper Cross-Slide. Bottom of compound and top slide of compound. The taper could be loose spindle bearings or a bad live tailstock center if you still get a taper when you are using the tailstock if you have it aligned right. It could possibly be the bed too. Hard sometimes to tweak in a Grizzly.
I would be happy to walk you through this on the phone if needed 651 338 8141 if I'm not to busy when you call. I am a journeyman machine tool rebuilder
Take it slow and check everything and don't assume the drilled and tapped all the holes correctly, used the right fasteners. Good Luck, Richard

 

[Tony Wells]

Good points, Rich. I've seen people drop a ball bearing into the hole on a set screw type gib adjustment. I suppose that would be telling, but I would rather see it fixed correctly. That sort of gib should have the shallow holes in it to prevent sliding.

 

[jayriz]

Be sure to check the 3 hex head screws that bolt the compound retaining ring to the compound.
They are usually loose and are not very good bolts to begin with.
Grade eight button head screws will go a long way towards stiffening it up.

Geno

Yea, those are solid, I replaced them when I built the beefier 4 point ring for it. There is no movement there, there is a few thous of rocking between the actual slide lower half and the upper half (the sliding half.

12bolts,

I initially described it a little wrong by saying the gib set screws where on the bottom half. I have attached a pic for clarity. Note, this is not my lathe or pic, I have just used it for the purpose of drawing on since it would be quicker than taking new photos. The circle is just to note where the movement is and the line drawn is to simulate where the gap appears when rocked (between the two halves). It isn't much, just a few thous, but that is enough to effect the finish.



ScrapMetal,

After I shimmed out the lathe again and ensured it was level I just tested it, and it still creates a taper. I've ran my dial indicator (anchored to the cross-slide) down a straight bar that has been centered using a 4 jaw chuck and centered at both the chuck end and holds center at the unsupported end while manually turning (left off tail stock just to see for sure) and it test dial holds 0 while moving the carriage up and down the stock which should mean the tool should run even up and down the stock and cut even. However, it still gives me a taper on this longer stock. I normally turn small parts on this thing and now that I'm using a longer piece of stock that requires some precision I'm just noticing it and I'm baffled how the taper could be introduced. I'm going to test again with the lathe running and make sure centripetal force isn't throwing the end out a bit causing the taper but I suspect it will be true because it is being supported.

Sorry, this sounds like I'm trying to throw a bunch of issues into a single thread, but I swear this isn't my first rodeo but I've only recently started using this 9x19 lathe for more stuff now and trying to clean it up.

 

[jayriz]

All, thanks for the info/replies.

Richard,

Thanks for the info and offer. The gib adjustments are definitely engaging because when I tighten them down the compound cannot be moved, but perhaps not all of them or more importantly the one closest to the tailstock (when setup at 90 deg) since that is where the gap is the largest when flexed. I will go out in the shop and inspect it further in the AM and give a report back and maybe get some pics of it disassembled.



Thanks,
Jason

 

[swatson144]

My 9x20 has pins that go between the gibs and set screws. They drop into a hole and act as pistons and are pretty trifling. Sometimes they stay in place on disassembly and sometimes they fall out and are small enough not to notice but easily replaced with music wire.

Quick check would be locking down the compound with each gib screw and seeing if one or more has no effect.

Steve