Emco Unimat 3 Threading tool

Hi all,

I just bought an Emco Unimat 3 to turn up some parts I need for a restoration - have to do this a couple of times a year.

I need to make fine aand coarse thread in both LH and RH on 3mm shafts.

Looking through the manual, this machine doesn't have the threading guide that's needed. Rather than go looking for a second-hand geared machine (workshop space)

Is there a source for second-hand bits and pieces for this lathe? At the moment, I'm looking for a threading kit in metric (preferably) as well as a dividing head.

Regards,

A

Just keep an eye out on e-bay though the threading attachments are less common than the dividing one and they don't come up that often. Also look in at Neils machines

A tailstock die holder would probably do most of your needs unless they are non standard pitches for a given diameter. I don't think they ever did left hand guides but I suppose you could get someone with a larger screwcutting lathe to make you some and matching followers once you find an attachment. Also worth noting that the finest pitch they did the metric guide sin was 0.5mm

I seem to remember seeing a couple of geared screwcutting designs for the U3 over the years which may be something to think about or even an small electronic lead screw

Edited By JasonB on 28/12/2022 07:58:27

Couldn't edit the above with apologies.

Did a thorough forum search before posting.

Came across nielsworkshop and penny-farthing.co.uk.

Any others?

A

Also see my edit about pitches

The easiest option if you only have a small number of thread sizes you plan to do is buy some suitable dies and make a tailstock die holder. There are plenty of plans and videos on this tool. I don't know if a Unimat threading attachment allows left hand thread cutting. If it does not then once again a tailstock die holder with a suitable die would be the best option. The other options of going down the ELS or full CNC route would probably be overkill for this small lathe with a small, specific, need. I have a friend who does restoration work on music boxes with a Unimat and this is his method. Anything bigger or odd I do for him.

Martin C

Thanks Jason. It's got an electronic lead screw, so was thinking of having a go at it that way too. (Great minds or fools....)

I'll look into the geared designs, hadn't thought about that.

I'm thinking the cheapest option is a tiny 'optimum type lathe second hand with back gearing, but space is a challenge.

Was thinking about cutting the LH thread with the feedscrew in reverse. Need to have a close look at the machine first.

Appreciate the time you took and the reply, as well as any other advice you or others may have.

A

Thanks Martin. The dies and tap are expensive (acme M3 x 1 or standard M3 x 1) but it's in the back pocket as a last resort. I was using tailstocks in 4' lathes to cut threads with a die in the early 80's.

Might have the wrong machine here and may need to bite the bullet on a CNC or back geared lathe.

If I read correctly, are you saying that your friend cuts simple threads with a tap/die and outsources complicated ones to a machine shop?

A

Regards,

A

Andrew F,

If as you say, the lathe is already fitted with an electronic leadscrew, surely you're all set to go. The major problem from my point of view would be obtaining, or more likely, grinding suitable tools to cut an ACME thread of 3mm diameter. Left or right hand threads are a breeze with the ELS.

John

As John says if you have the ELS then best to use that as you won't find dies right hand to cut M3 x 1 in any profile let alone left hand as it's a very coarse pitch, standard for M3 is 0.5mm pitch.

Even with an ELS M3 x 1 on M3 stock particularly ACME will be a real challenge as the minor diameter is going to be very small and weak. Should that be trapizoidal rather than ACME form as you are using metric sizes?

Thanks John.

Yep Jason. My error. I've got a heavily (axially) loaded shaft. Trapezoidal will be better as you say, it's metric standard. I thought of this after posting, and was just mulling over the design as you replied. 1mm minor diameter is lunacy.

Biggest issue is going to be grinding the internal thread cutter for a small dia internal thread to match the external thread, then cutting it. A square acme thread was my call there as 90° is easier to grind. Ease of use vs ease of manufacture.

Still finalising design issues on this one.

My biggest concern is that I've got to make this in spare time for delivery in 3 weeks, with the lathe arriving 3 Jan. It'll be tight.

You've all given confidence that I can use the electronic feed to cut this, having not seen the machine yet. Thanks.

Will post results.

Edited By Andrew F in Australia on 28/12/2022 10:37:39

Andrew, I am a hobby machinist so I would not particularly say my friend out-sources to a machine shop but in effect that is what he does. Most of the music boxes he restores are European so generally the screw threads are small metric standard but there are some unusual threads occasionally appearing. The last thing I did for him involved making some Ø7x1.1 Lowenherz form screws (once I had identified the thread form). Not something you will easily find dies for and an unusual pitch as well. These were not part of the music box mechanism but were for holding the case to the main frame.

You can see the sort of music boxes he restores if you search for "Antique Mandoline Piccolo Music Box by Paillard, c. 1880".

Martin C

Even a square thread at 1mm pitch on a 3mm shaft will be a challenge, the tool won't be a simple 1mm parting tool shape but will need a lot of clearance so that it does not run on the high helix angle of the thread.

As for the even more difficult internal thread to match you would probably be better off making a very long tap with a fine taper over many turns of the thread rather than trying to single point cut the thread.

One option for cutting a square thread would be to mount the U3 milling head onto the carriage (if you have the head) and then directly link the spindle with the 1mm pitch lead screw and rotate the lead screw while milling with a 0.5mm milling cutter. Probably easier to rig up a steady for this type of cutting too rather than a traveling steady for more conventional screwcuting as the work is likely to deflect whatever way you try and cut the thread.

Mention of ACME above reminded me that there is stub ACME.

In the same way, there is stub trapezoidal to DIN380.

Unfortunately, it does not go down to 1mm pitch, but you could take the proportions and extrapolate them. That might help with the minor diameter issue.

The best image I found of the dimensions is here (open image and it is a little bigger, just about readable if you zoom in):

https://webstore.ansi.org/cover-pages/small/DIN/2000517.jpg

Thanks DC3ik, Am going to look it up.

Really appreciate the time you spent on this.

Regards,

A

Hi Andrew

Are you aware of the Unimat groups on groups.io? The biggest is groups.io/g/Unimat which is nominally for DB/SL models but has a lot of U3 owners, whilst groups.io/g/Unimat3 is smaller but just for the 3. Both groups are public so you can "try before you buy".

This post looks particularly relevant to your needs, being a way to fit screw cutting gears to a U3. If you have access to a 3D printer you could create the necessary gears in Fusion 360.

Brian G

Thanks Brian,

I wasn't but have joined.

The back gearing post is excellent.

A