Unimat 3 saddle gibs

[Julius Henry MarxParticipant @juliushenrymarx92355]

Hello:

Posted by Julius Henry Marx on 15/06/2023 02:48:45:

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

Best,

JHM

[Julius Henry MarxParticipant @juliushenrymarx92355]

Hello:

Posted by Graham Meek on 15/06/2023 11:29:17:

… OP says he uses Carbide inserts.

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

… provided the insert radius is not too big. I only use 0.2 mm radius inserts …

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

[HuubParticipant @huub]

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.

[Kiwi BlokeParticipant @kiwibloke62605]

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!

[Julius Henry MarxParticipant @juliushenrymarx92355]

Hello:

Posted by Kiwi Bloke on 20/06/2023 21:36:43:

As Michael Gilligan has pointed out …

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

Best,

JHM

[Kiwi BlokeParticipant @kiwibloke62605]

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.

[HopperParticipant @hopper]

Perhaps the mods should merge these two threads into one?

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