kinda reaching here but is the gib straight and sides parallel and are the angles for the dovetails matching? I was wondering if you were using actual Hi Spot Prussian blue I'm not sure if magic marker would show what's happening. Another out there suggestion would be to make sure the edges of the gib or the dovetails aren't bottoming there should be some relief either on the edge of the dovetail or at its root, if that makes any sense?
Lathe slide wobble
- Thread starter syrtismajor
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jack620
Well-Known Member
It's difficult to visualise how the forces act in that arrangement, but to my eye the gib screws will tend to push the gib up.
Except the gib screws will chew the back side of the gib. The damage will have to be stoned out if the gib is to be returned to its designed orientation. And if your Boxford engineer friend is right about the pockets being there to keep the gib from slipping out, what will prevent this from happening if the gib is reversed?
jack620
Well-Known Member
goldstar31
Well-Known Member
My copy of Connoly's Machinery Tool Reconditioning is almost 600 pages. You have done well
Well done
Norman
goldstar31
Well-Known Member
Have you returned to real world Norman? Welcome back!
You are wrong- sorry but playing about in a little workshop is NOT the real world. The REAL world is - and always has been a horrid place. This is why part of my family went to Orange and then to Tumba Rumba in search of a better world. Uncle Harold went out because there was no job when he was out of his time as a carpenter. The news broke that Nestle was to close its factory a mile or so away from here and 456 workers will be looking for work. Some are friends- and it hurts.
Yesterday, I sort of lived on the phone and I'm sort of attached to blokes who take cancer patients to and from hospital. Yes, it needs money and modestly 'Yes' My wife died of cancer!
We in the UK are finally working our way out of Covid-19 and Astra Zeneneca is 'doing its stuff 'Worldwide'- for no more than production costs. I can write another "Yes'-- and why not be thrilled.
Children in the UK? Many are starving. Modestly - again 'Yes' and a nice little what the masons call a 'jewel' and I'm now a Grand Patron of the Charity. I'm now almost comoletely blind in one eye and the remaing one is constantly being 'jabbed' so that I can have a bit od 'displacement therapy' in my shed.
I cannot change the World but perhaps for some less fortunate, I have mumbled "yes'
'Model Engineering'? It's a game
So as a very minor Provincial Grand Lodge
Officer 'I greet you well'jack620
Well-Known Member
Much of the world is horrible Norman, but not the part you or I live in. And Orange is very nice, so your family chose well.
Chin up. I hope to attain your ripe old age, although I don’t like the idea of having my eye jabbed.
olympic
Well-Known Member
Just my $.02 worth:
After reading all this yesterday, I went down to my shop and really looked at my second-hand Craftex B2071 Chinese lathe/mill combination (please don't laugh; I'm very sensitive about this
), whose saddle has been shifting unpredictability ever since I got the machine, forcing me to make .005" cuts even in aluminium to avoid serious chatter.
Like everyone else, I think, I kept tightening the gib screws till nothing would move at all, but that didn't work; I could still shake the saddle by hand.
After reading here about how tightening changes the relationship between the gib and the slide, I tried loosening the gibs just a tad.
And it worked! No shake, rattle and roll.
I dunno....
After reading all this yesterday, I went down to my shop and really looked at my second-hand Craftex B2071 Chinese lathe/mill combination (please don't laugh; I'm very sensitive about this
), whose saddle has been shifting unpredictability ever since I got the machine, forcing me to make .005" cuts even in aluminium to avoid serious chatter.Like everyone else, I think, I kept tightening the gib screws till nothing would move at all, but that didn't work; I could still shake the saddle by hand.
After reading here about how tightening changes the relationship between the gib and the slide, I tried loosening the gibs just a tad.
And it worked! No shake, rattle and roll.
I dunno....
jack620
Well-Known Member
Just to clarify here, the saddle rides on the bed/ways. The cross-slide rides on the saddle. If you can shake the saddle by hand I don't think the gib screws are the issue (despite what loosening the screws may have led you to think). There's something else going on.
My lathe has a plate on the underside of the saddle that clamps the saddle to the underside of the ways. It must be adjusted so the saddle is vibration-free but not so tight it won't move. Does you lathe have such a retaining plate?
When I lock my cross-slide with the gib locking screw I fitted, the saddle and the cross-slide become 'as one' and there's no movement between the two. It makes no sense to me that tightening the gib screws reduces the rigidity. Unless your cross-slide is so flimsy that tightening the screws distorts it to the point it is no longer a good fit to the saddle.
olympic
Well-Known Member
It's not the cross-slide here, it really is the saddle.
As I said, "I dunno," because I really don't. In any event what I did worked.
As I said, "I dunno," because I really don't. In any event what I did worked.
goldstar31
Well-Known Member
Last edited:
terryd
Well-Known Member
Hi
Round ended grub screws will cause very little damage and if they do you are tightening them up too much, they should only be tight enough to prevent play in the slideways. Besides, it is not a great deal to 'stone out' a few marks from an experimental test. Note the word 'experimental'. If as you say the screws will make their own 'pockets' that is what prevents the slippage and some manufacturers use a pinned key,
I admit that I don't quite have 60 years experience. only 58 but that is on a wide range of machines. Lathes from small precision to large vertical ones capable of machining the rim of a cast hopper bell for a blast furnace to a lathe from the Austin Motor company built in 1904 ready the opening of Austin in 1905, (the date of manufacture was cast into the machine shell). I've also worked in toolroom and production situations on a variety of machines including shapers and 24 foot planers making brake press tooling. So what do I know about it? Obviously not much compared to many on here.
Stay safe and healthy
TerryD
jack620
Well-Known Member
Perhaps not, but if you refer to post #4 the OP said his gib originally didn't have pockets, so he added them. So he already knows the experiment you suggested won't help.
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So more back-to-basics here: Skip this if I'm preaching to the choir.
There is "checking" for looseness for movement, then there is "mechanic's feel," then there is critical feeling and measuring.
One needs to practice the technique of moving something carefully, with barely any large-muscle engagement. If one holds on tight and tries to move something with all their might, the nerve endings will not be sensitive to small motions. This is a skill worth developing, but it is in the realm of techniques that take a while to learn, but stay with one once learned. An an example of an equivalent skill and technique is hand-sharpening things: It is rarely learned in one step, but is worth learning over time.
If one has the "feel" for fits and motions, it goes a long way toward getting to the root of problems like the one(s) under discussion.
There is also the need to know how the machine under test is constructed and to think through the possible places to look for play and consider what may be out-of-adjustment, or needing modification.
That said, there may also be the need to move on to measurement. In measurement, there is usually only one dimension of movement to check at a time, with careful thought as to what is actually being measured.
So, on my mini-lathe, I carefullly try to move and feel for motion of the compound relative to the cross-slide, then tighten the screws slightly and do the same check again. Rinse and repeat. Then I move on to the cross-slide and repeat everything again. then I move on to the Saddle and do it again. Then, when I thiink I have the problem isolated I apply the indicators, etc and check again.
Now, if I have isolated the problem, or the worst of the problems (which is what one does with an inexpensive machine), I take things apart and start measuring parts the best I can with the tools I have. The how-to-do-it of these measurements are explained in Connelly and other books.
There are measurements of a part with scale, square, micrometer, etc.
There are checks for straightness and squareness against standards like parallels, squares, and surface plates.
There are checks for fit with guages, shims, and dyes.
After all that, there may be the chance to do a modification, but tread softly and keep checking.
Of course, there are also the issues relating to mounting the machine, leveling it, and using it within its limitations.
What one finds with an inexpensive machine is that there is always room for improvement and one generally works through tests and problems in a spiral that gets progressively closer to having a well-adjusted and precise machine. What one also finds is that one will eventually get to the place where not much more can be done and "better" is probably a better machine: I still have my Mini-Lathe, but I can't turn it into a Monarch or a Hardinge. I just have to work around the problems with what I have.
Again, apologies for droning on with this.
--ShopShoe
There is "checking" for looseness for movement, then there is "mechanic's feel," then there is critical feeling and measuring.
One needs to practice the technique of moving something carefully, with barely any large-muscle engagement. If one holds on tight and tries to move something with all their might, the nerve endings will not be sensitive to small motions. This is a skill worth developing, but it is in the realm of techniques that take a while to learn, but stay with one once learned. An an example of an equivalent skill and technique is hand-sharpening things: It is rarely learned in one step, but is worth learning over time.
If one has the "feel" for fits and motions, it goes a long way toward getting to the root of problems like the one(s) under discussion.
There is also the need to know how the machine under test is constructed and to think through the possible places to look for play and consider what may be out-of-adjustment, or needing modification.
That said, there may also be the need to move on to measurement. In measurement, there is usually only one dimension of movement to check at a time, with careful thought as to what is actually being measured.
So, on my mini-lathe, I carefullly try to move and feel for motion of the compound relative to the cross-slide, then tighten the screws slightly and do the same check again. Rinse and repeat. Then I move on to the cross-slide and repeat everything again. then I move on to the Saddle and do it again. Then, when I thiink I have the problem isolated I apply the indicators, etc and check again.
Now, if I have isolated the problem, or the worst of the problems (which is what one does with an inexpensive machine), I take things apart and start measuring parts the best I can with the tools I have. The how-to-do-it of these measurements are explained in Connelly and other books.
There are measurements of a part with scale, square, micrometer, etc.
There are checks for straightness and squareness against standards like parallels, squares, and surface plates.
There are checks for fit with guages, shims, and dyes.
After all that, there may be the chance to do a modification, but tread softly and keep checking.
Of course, there are also the issues relating to mounting the machine, leveling it, and using it within its limitations.
What one finds with an inexpensive machine is that there is always room for improvement and one generally works through tests and problems in a spiral that gets progressively closer to having a well-adjusted and precise machine. What one also finds is that one will eventually get to the place where not much more can be done and "better" is probably a better machine: I still have my Mini-Lathe, but I can't turn it into a Monarch or a Hardinge. I just have to work around the problems with what I have.
Again, apologies for droning on with this.
--ShopShoe
That happens on China made.
Basically the jib is to wide and or drill worng. Both easy fix. They also will make the dovetail to wide too.
Dave
Basically the jib is to wide and or drill worng. Both easy fix. They also will make the dovetail to wide too.
Dave
terryd
Well-Known Member
Hi,
I answered how that might cause a problem in an earlier posting, it depends on how he determined the position of the 'pockets' and how deeply they are drilled obviously the manufacturersdecided that they were not needed.
Just for your interest here is a traditional gib key without 'pockets - it's even older than me
You can see the witness marks made by the grub (set) screws - there are two distinct sets, probably someone put the key in 'upside down' at some time. The centre channel is semi circular in profile to accommodates an extra grub screw with rounded end and this is to prevent any slippage of the key during operation not to aid clamping.
Stay safe and healthy,
TerryD
goldstar31
Well-Known Member
Where there should be a 'dimple' on my Myford-- there isn't.
It acts as a lock.
It acts as a lock.
jack620
Well-Known Member
Being Chinese I reckon it's more likely they decided they could save money by not adding them.
What's the gib in the picture from?
They nothing from China that is ready out the box.
But low in cost with fixing
Dave
But low in cost with fixing
Dave
Being Chinese I reckon it's more likely they decided they could save money by not adding them.
What's the gib in the picture from?
There is some confusion here. The saddle doesn't have gibs. It runs on the bedway. Moot point if you are happy with your lathe now.
