Group meeting

[Steve HuckinsParticipant @stevehuckins53362]

Beginner lathe

[Steve HuckinsParticipant @stevehuckins53362]

Hi to all.

I am new to machining (Sieg SC4 currently) and would like to enjoy getting together with other enthusiasts somewhere near Exmoor. Are there any clubs or meets near enough for me to visit and hopefully join ?

Exmoor oldie

[Howard LewisParticipant @howardlewis46836]

Google "Model Engineering Clubs" in your vicinity

Hopefully, you'll find some. Go and join!

In my book you have a good machine which should keep you happy for many years.

You will find a set of Zeus Charts very useful.

You will need equipment to measure what you are making.

A 3 jaw chuck will not provide absolute concentricity. It can produce diameters which are concentric to each other, but not necessarily to the raw material, if they are all machined without disturbing the raw material in any way.

To minimise eccentricity, you will need a 4 jaw independant chuck, a magnetic base and at least one Dial Test Indicator.. A plunger type DTI may be graduated in 0.01 mm units, (sometimes coarser ) where a finger type DTI is likely to have 0.01 mm graduations. Both have their uses (A Finger clock can be used to check concentricity of a bore, which a plunger type cannot

If you haven't already got any, buy and read some of the books on using a lathe

L H Sparey "The Amateur's Lathe", Stan Bray "Basic Latework", Harold Hall "Lathework",. Neil Wyatt has written a book on his experiences with the SC4, One or more will be of use to you..

You may find Ian Bradley's "The Amateur's Workshop" helpful, also. Especially if you want to set up the lathe, as well as other workshop practices..

As a refrence book, you will find Tubal Cain's "Model Engineer's Handbook" useful.

As you gain experience, you will find a use for other books from the Workshop Practice Series.

FWIW, become familiar with the lathe. Don't rush into making a complicated model. Make your mistakes on relatively cheap bits of mild steel rather than an expensive casting from a kit.

When you come to making threads, you are likely to be using Taps and Dies for much of the smaller, < 12 mm, sizes. When threading upto a shoulder, or down a blind hole, a Mandrel handle will be useful. You produce the low speed required, rather than the machine.

You will do less damage that way. Broken taps are almost impossible to remove, so the part will be scrap!

Usually the very last hole that you are tapping, so a lot of work wasted!

You will need a Tapping Compound for thread cutting; Trefolex or Rocol RTD.

Again, making a sliding Die Holder (You can buy just the actual Die Holdes and make the body, if you wish ) The Die holder slides on an arbor, held in the tailstock.

It will be worth making a Tap holder to slide on the same arbor.. A quick way is to mount a small drill chuck om a body. After all you are unlikely to find many Taps with a shank bigger than 12mm.

Using the thread as it is being cut, to drag the tai stock along the bed is likely to damage, or strip the thread, especiall small,or fine, threadsl

So, if have not already got some, you will need drills.

Riding my hobby horses, make a Centre Height Gauge. Once set, this will help you to set tools on centre height, so that no pip is ptoduced when the tool comes to the centre of the work.

Most of the books mentionjed above will give tips on grinding tools.

Another hobby horse of mine is to use a Tangential turning tool for a lot of my work. (Only one face to grind, using a suitable jig )

Carbide tips have their uses, but you can regrind a blunt HSS tool at 9:00 pm on a Saturday night, when you have just chipped your last carbide insert! But HSS will have difficulty cutting hardened steel!

As ever, Horses for courses!

Hope that all this rambling is of some help rather than teaching granny to suck eggs.

Howard

[BazyleParticipant @bazyle]

There has been a small group in the Barnstaple area but I'm not sure what their status is currently. Otherwise there is Exeter and Tiverton. The L&B railway also will have some machine oriented members. There are Men's Sheds at Torrington and Okehampton and I think one is starting up in or around Bideford,

[Steve HuckinsParticipant @stevehuckins53362]

Thanks for the info so far and hopefully there may be other replies to come.

One piece of advice I would like to ask :

I turned down some brass to size and threaded an internal and external to M10 x 1.0 metric fine using taps and die.

The dimensions for the screw thread and drill hole I took from the charts,

Nice finish on both parts but… the fit was quite" sloppy". I would have expected a nice firm fit with little or no play.

Any ideas ??

[Michael GilliganParticipant @michaelgilligan61133]

Steve

It will depend, amongst many other things, upon which of “the charts” you chose

Quoting from Wikipedia:

Tolerance classes defined in ISO 965-1 can be appended to these designations, if required (e.g. M500– 6g in external threads). External threads are designated by lowercase letter, g or h. Internal threads are designated by upper case letters, G or H.^[4]: 17

MichaelG.

.

Ref. https://en.wikipedia.org/wiki/ISO_metric_screw_thread
 

… enjoy the journey.

Edited By Michael Gilligan on 30/07/2023 13:54:44

[Mike HurleyParticipant @mikehurley60381]

Were you using brand new taps and dies or ones previously used on steel? Also, what sort of dies are using – split or fixed? Don't know your level of experience, but in case you aren't familiar you can adjust the fit of the male thread portion by adjusting the split die appropriately

Regards Mike

[Steve HuckinsParticipant @stevehuckins53362]

Cheers for the responses.

I did use a new split Die in the fully open position and a new set of 3 Taps in order.

I used the chart for metric fine where tapping drill for M10 x 1.0 was 9.0 mm for the internal thread and obviously turned the screw to 10.0mm for the external thread. By hand not under power. Cutting fluid used and tail stock to square up taps and tailstock die holder etc.

I will look into the info Michael G supplied earlier on ISO.

Regards Steve

[SillyOldDufferModerator @sillyoldduffer]

Posted by Michael Gilligan on 30/07/2023 13:52:55:

Steve

It will depend, amongst many other things, upon which of “the charts” you chose

…

+1 From memory most charts are for less than 80% engagement.

Cutting tight threads puts progressively more stress on taps and dies causing rapid wear and breakages. As high engagements aren't much stronger than 80%, and are more hassle to fit because alignment is critical, most threads are generally made on the loose side unless there's a specific need for tightness.

Brass and a new die should cut to size without bother, otherwise I'd suspect an unfriendly material and/or blunt cutter.

M10 x 1.0 into a 9.0mm hole gives a 77% engagement. An 8.9mm hole gives 85% engagement., and 8.8 provides 92.4%. For real men only, an 11/32" tap drill gives 97.7%. Not recommended – over 90% the risk of breaking the tap shoots up, as does the chance of the thread veering off axis.

As Model Engineers hate spending money, it's not unusual for us to keep well below 80% engagement. Mollycoddled taps and dies last much longer.

Dave

[Steve HuckinsParticipant @stevehuckins53362]

Dave thank you for information I had no knowledge of. I may try your 8.9mm option to experiment with how the thread feels. I am grateful for everyone’s help and advice. I hope to stay plugged in to learn more from you all. No projects as such yet but practising using the lathe.

Regards Steve

[BazyleParticipant @bazyle]

Steve, If you are still looking for engineering contacts the Tarka Line (full size) are having a grand reopening event on Saturday at Great Torrington.

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