Gib adjustment on SX2 P mill

[John Gray 7Participant @johngray7]

I noticed the other day that when the Z axis is zeroed on my dro, tightening down the head with the Bristol type lever alters the reading by a small amount, maybe 0.1 mm max. I’m presuming this is a gib issue so I was going to have another go at adjusting them. The mill was new from arc maybe 6-8 months ago and although I have adjusted all the gibs at set up I seem to remember quitting on the Z axis as it is to me difficult to get at without the various other bits of metalwork getting in the way. My question is, does anyone have a good workaround to deal with this. I was thinking of perhaps a thin walled short box spanner that could hold the locknut in position and operate the Hex key through the middle ?I have tried to use a socket to do this but it’s too bulky and fouls the other metalwork. There appears to be 4 gib screws, some are slightly better than others to get at, but non are wonderful. Must be loads of these machines with our members and I’d hate to think I’m the only  person with this issue. I have this evening reached my patience limit trying to adjust the top gib which I think might be one of the easiest of the 4, using the supplied 10mm open ended and a hex key. I nipped up this gib by a tiny amount and now the dro reading is not changing when I lock it, so I recon I’m on the right path, and it’s worth trying to do the other 3. How do you do yours?

John

[Michael GilliganParticipant @michaelgilligan61133]

It sounds like you have re-invented the SPQR Tappet Adjuster, John

… a jolly sensible idea, I would think

MichaelG.

[PeteParticipant @pete41194]

I found that just removing the coarse pillar / drill press type down feed handle made seeing what your doing and making any adjustments a lot easier. I’m not sure if there still available or even called the same thing today. But in North America, I have a set of what are called Ignition Wrenches. Once used on old school automotive ignition components, there much thinner in cross section than the more standard size wrenches, and those work well for these gib adjustments. If the design hasn’t changed, the second gib screw from the top is the worst one on mine for access.

But I’m unsure of how your adjusting those Z axis gib screws. Yours might be different, but mine uses Allan head set screws as the adjusters and thin locking nuts. Since the nuts play no part in the adjustments, I just back them all off a couple of rotations, adjust each of the set screws until I have the slight gib clearance I want, then use an Allan wrench on each set screw to prevent any further rotation or movement, spin each nut in with a finger tip, and do the last final tightening with the wrench. Those nuts shouldn’t be tight as the adjustments are made. So I’ve never thought anything more complex was needed. All those locking nuts do is prevent the set screws from loosening due to vibrations and hold each adjustment screw in the position there set to against the gib. Final tightening of each nut can sometimes slightly alter the adjustment, so a bit of back and forth might be needed. Compared to a tapered gib design it takes much longer to get correct, but not impossible to work with. Luckily it doesn’t need doing very often.

I could be wrong, but something also doesn’t sound right with the mounting of your dro scale and reader head. Tightening that Bristol / adjustable locking handle that’s 90 degrees to the Z axis scale movement shouldn’t show a vertical position change. Once your Z axis gib is properly adjusted, I think I’d put an indicator against the scale and check for any movement as that slide locking handle is set and released.

 

[John Gray 7Participant @johngray7]

Thanks for the replies. Pete hey I remember ignition spanner’s! Not sure they would help on this case though. The coarse downfeed does get in the way a bit, but so also does the gas strut that arc fits to both sides of the head.there is a lot going on in the vicinity of these gibs, and I recon they are always going to be awkward at best. You are right theses adjusters are an Allen head set screw with a nut to lock it in place. Access to the locking nut to loosen and lock the adjuster is the main bit that is causing me a problem and I just thought someone may have a smart way round this. It is possible that earlier machines that did not have the twin gas struts do not have this problem. I’m away from home at the moment so I can’t just pop in an see exactly what is stopping my easy access. When I return home I intend to source some box spanners and cut them down so that I can pass an Allen key through the centre, hold the set whilst tightening down the locknut, I’m hoping this will solve my issue, but I can’t really tell until I can get home and have another look. On the X and Y gibs I have placed a split spring washer under the lock nut and having set the gib on the adjuster, just snug down the locknut to apply pressure to the spring washer. This has worked well and has not moved due to vibration and I recommend it. I cannot claim I invented this I’m sure I read it somewhere but I’ve no idea where.

[PeteParticipant @pete41194]

There were no gas struts on mine, so I can imagine access for yours is a lot more restricted John. More added work, but you may need even further disassembly. Fortunately the adjustments don’t need doing too often, but even for mine I thought it was a poorly thought out design.

[Michael GilliganParticipant @michaelgilligan61133]

SPQR launch:

https://archive.commercialmotor.com/article/31st-october-1969/71/tappet-tool

Sorry … haven’t found any drawings, but that ^^^ might trigger some memories.

MichaelG.

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Edit:

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credit https://www.mgexp.com/forum/mgb-and-gt-forum.1/spqr-tappet-adjuster.2259492/

 

[John Gray 7Participant @johngray7]

Just for completeness and for anyone with a SX2 Mill and an interest in setting the Z axis gibs, I have tried my box spanner method and can confirm it doesn’t work! Sure I can get hex key through the centre of the box spanner, but with one exception, I cannot get the spanner on the lock nut. As has been suggested, some partial strip down is definitely required, at very least removing the gas strut on the gib side, and possibly the three levered coarse down feed handle. On the plus side, I have got a result by snugging up the 1 gib I could get to, and making the discovery that if I back off the fine feed wheel to the loose part of the ridiculously big backlash that comes for free with these mills, and then lock the head, all is well. No movement on the  DRO screen, which reads the same at the end of the cut as it did at the start. The play in the fine feed mechanism seems to be the cause of the movement observed on my Dro and is now easily worked round. Squaring up material is working very well. If I ever need to adjust the Z gibbs in the future, I recon I’ve got a bit of stripping down to do first. I can’t see any way round this.

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