Unimat 3 saddle gibs

We have just made a brass gib for the longer cross slide on the Atlas 12 x 24 lathe, it was the best size laying about and quite good. The original looks like cast iron, and if I had a choice some bronze woulf have been used. The aluminium might wear faster, but if it is available and can be adjusted easily, I see no reason not to use it. Keep the bed clean and oiled and all should be well.

Hello:

You sir are undoubtedly both a brave (and knowledgeable) soul! 8^D

Interesting. (warnings have been taken into account ...)

Am I correct in assuming you are measuring the 'tilt' from/between front to/and back?

I think that is the hardest part to get right.

Could the milling column vee block (on the back of the bed) be used for the magnetic base?

When I am through with all the pending stuff I will have a go at the measuring part of the procedure to see exactly what is going on.

Not having a reliable idea of the situation is a sure recipe for going around in circles.

Thank you very much for your input.

Best,

JHM

You can measure the tilt using an indicator but you probably feel the headstock/saddle/tail stock rocking when pressing on one of the four corners. Weep off any oil because that influences the measurement.

You have to check the tilt of the headstock at its mounting position.
You can check the tilt of the saddle/tail stock on any position of the bed. I used the end of the bed because that is worn the least.

The hardest part to get right is the head stock alignment. Once the head stock isn't rocking any more, you can adjust the alignment. For that you have to remove metal on two places so the headstock doesn't start rocking again.
For changing the up/down angle, you have to remove metal on the front or the back (flat side and both sides of the V).
For changing the left/right angle, you have to remove metal on 2 opposite sides of the V.

Because you don't remove much metal, It is a slow process so it takes a lot of trials to see a change in the alignment. That also means that if you remove the metal on the wrong side, you only slowly increase the error.
You need to keep the test bar in the head stock/chuck for checking the alignment. That makes the head stock quite heavy.
I used a self made test bar because this test bar has no runout and that makes checking the alignment easier.

Once the headstock is aligned, you can align the tail stock.
Some lathes have a headstock that allows changing the left/right angle by rotating the head stock around a swivel point.

If you bolt your lathe to a rigid stand, you can twist the lathe bed causing mis alignment. So my mini lathe and bigger lathe are not bolted to the stand.
The rigidity of my bigger lathe would surely benefit from bolting to the stand but the concrete floor would influence the lathe alignment when the temperature changes (summer/winter) and that is a no-go for me. My shop is on the first floor (pre tensioned concrete plates)!

Not if you do it correctly and put shims under any of the lathe feet that are not in contact with the base before tightening down any of the bolts. Here is a description from the Myford manual on how to do it, and how to use a dial indicator to make sure there is zero distortion of the bed when bolting it down. See Fig 19 and text below that.

Hello:

I think that the original topic ie: question about lift plate material has been answered and it would be a good idea to split this post to another, related and equally important topic.

I went to my usual purveyor of plastics and non-ferrous materials today and got a very good deal on a few left over bits and pieces, one of which was a length of 5/8" x 5/32" brass, more than enough to make myself a new pair of lift plates to replace the ca. 1980 Emco issued ones.

Then I started on Kiwi Bloke's suggestion which I think merits its own thread.

Thank you all for your input.

Best,

JHM

Edited By Julius Henry Marx on 15/06/2023 02:50:36

Edited By Julius Henry Marx on 15/06/2023 04:14:02

Fitting of the strips seems related to the choice of material. Bit of brass should work for you. I vaguely remember on one "microlathe" I fixed up for a bloke a few years ago it did perform better when we set up the lift plate strips (steel from memory) so they were a neat sliding fit on the underside of the way where they run. Blued them up to just contact and that is all. Had to rub a few high spots down on the ways with a fine flat file and rubbing stone. In theory the lift plate should not affect cutting but in practice it did seem to help on these rigidity-challenged tiddlers.

Edited By Hopper on 15/06/2023 08:40:53

.

I suspect that the lack of mass in the saddle and its attachments might be a major contributor to the problem … a big lathe has lots of inertia there, and the saddle is well-behaved on the inverted vees.

Could we be in one of those “you can’t scale Nature” situations, I wonder ?

MichaelG.

The OP says he uses Carbide inserts. There is no problem with this provided the insert radius is not too big. I only use 0.2 mm radius inserts on my Unimat. Using a 0.4 mm rad causes a lot of vibration and a poor finish.

The Compact 5 will tolerate the 0.4 mm radius with no problem. Having said that there is more contact area on the carriage. Plus the headstock bearings and spindle are more robust. It is all a question of rigidity with these small machines. The quality of the insert is another key player. They will seldom have as keen an edge as an HSS tool properly stoned.

The Unimat machine was designed in the early 1970's and it was designed around HSS tools. This was the tooling that Emco originally supplied. Emco did not start supplying Carbide inserts for the C5 until the 1990's.

Regards

Gray,

Hello:

I believe so.

Having read more than one post on various forums where it was stated that the change to brass strips made a noticeable difference, I look forward to being able to say the same thing.

No suspicion whatsoever on my behalf: I'm absolutely convinced that it is the major contributor.

Just the fact that a barely ill fitting set of lift strips will wreak havok to the simplest turning operation (eg: small diameter, short piece of plain aluminium) attests to that being so.

Like I mentioned earlier in this same thread: " ... how much effort was put into limiting the type and amount of materials used (eg: underside of the carriage (!), lead screw nut post, etc.) I am absolutely convinced that accountants and not engineers were in charge."

If it were only that (ie: scale) then the U3 would have a saddle cast from the same material as the bed and it would have a size/weigh/heft in proportion to the size/weight/heft of the bed, like most lathes seem to have.

Thank you both for your input.

Best,

JHM

Edited By Julius Henry Marx on 15/06/2023 12:28:24

Hello:

Best,

JHM

Hello:

Quite so. I purchased them sort of in a hurry, along with some much needed belting and tooling when I purchased my U3.

Ahh ... all the inserts I have are DCMT070204 / DCMT21.51.

From what I have read, the '04' is the radius and yes, quite a bit of vibration on the U3, now greatly reduced after fixing the carriage lift strips but still singing a bit when turning.

A question if I may: could you tell me what model/code inserts do you use with your Unimat?

I see that the same manufacturer (Mitsubishi) also has a DCMT070202 on their webpage for that specific product, but there are 13 (!) different options.

Ideally I would prefer to use that same shape as I already have a few holders.

Thanks in advance.

Best,

JHM

From Mitsubishi I use the DCMT070204 VP15TF inserts for steel. These are intended for finishing. DCMT070202 inserts have a smaller nose radius and will need less cutting forces. These inserts are also sharp enough for turning POM or brass.

For aluminium I use the uncoated ground inserts from Korloy DCGT070204 AK H01. These are also available as DCGT070202. These work also for POM and steel because the cutting forces are low due to the very sharp ground cutting edges.

As Michael Gilligan has pointed out, scaling things can cause problems. Remember that, as linear dimensions increase, mass increases with a cube law. Even though a larger lathe can take heavier cuts, I don't think cutting forces, which have to be reacted by saddle, etc., will increase at anything like the same rate. Therefore, in large lathes, the saddle's weight is a major component of its location and stability.

A little U3 is, one might say, too lightly constructed, and is not gorilla-proof, and nature's scaling law works against it. As Graham Meek has pointed out, the Maximat 11 has plastic anti-lift strips. I think the V13 also has. Neither is adjustable, IIRC. They probably contribute little to the stability of the saddle (under normal conditions).

On the U3, however, the anti-lift strips are vital, because gravity isn't doing enough to locate the saddle. They are non-adjustable (unlike the Sieg - interesting...), and it appears that saddle manufacture has, in their location surface's regard, wide tolerances.

This long preamble is to justify my belief that the choice of a plastic material by Emco is intelligent, not negligent. The strips are almost certainly designed to be elastic, so that they are in a sprung, pre-loaded condition when tightened down. Of course, when the saddle has been incorrectly manufactured (or horribly worn), there's no pre-load, nor even any contact, so they are ineffective. So the strips must produce a sufficient force on their ways to pull the saddle down onto the bed ways, doing the job that gravity can't.

Lubrication in this position is going to be hit-or-miss, so an inherently 'slippery' plastic is better than metal. Also, the increased stiffness of metal means that it won't act like a spring. Sieg's adjustable strip approach is necessary for metal strips. Emco provide no adjustment, so flexible strips are necessary in this application. Metal may be OK, if carefully fitted, but wear will destroy the fit.

Think in terms of pre-load. No movement is possible, until the pre-load force is exceeded, even if pre-load is provided by something floppy, like a rubber band!

Bottom line - stay with plastic, but make sure it is adequately pre-loaded!

Hello:

Please see the reply in my other thread about carriage rigidity.

Best,

JHM

OK, I took a guess as to which thread I should aim my reply - and got it wrong. (Life can be so confusing...).

Please see other thread.

Perhaps the mods should merge these two threads into one?