Member postings for douglas coates

New sums, I checked the current tap which is not exactly 4tpi. I've done a re-calculatiojn as I seem to get strange answers to the 2 diameters. If I set pitch at 6mm but with 1mm flat, the triangle is 5mm, so perpendicular is 4.33. According to that the I/D and O/D differ by 8.66 mm?? I can get a 35mm Forstner for the nut blank, and a 45mm for the vice guide which I can grind down to about 43.7 say. Which bits of this are wrong !!?

Edited By douglas coates on 05/05/2016 09:16:31

Thanks for all the knowledge and interest - various bits of feedback as far as I know them:
- relief - I didn't make the current tap or guide (I did make the cutter and box) but in these things the cutter depth is adjusted so the screw runs smooth but not sloppy (in the wood nut). I suppoose this has the effect of giving some axial clearance, but it's a bit more crude - pretty much everything is as we are dealing with wood, grain, atmos movement etc.
- the angle is definitely 60 degrees, pic is not very good, but I know from making the cutter
- my sums were rubbish, the current 4tpi uses a 35mm bit for female blank, and a 41mm approx dowel that the screw is cut from. I need to check the tpi, do we talk points or whole teeth?
- optimal tpi - from playing with many different wood screws for vices, I am sure on this one that my 4tpi is a tads steep, 6 is too fine, but best guess would be I'd like about 4.5 - 4.8.
- bad drawing, the thread is cut on axis, the taper creates progressive flats towards the leading end.
- rads and flats - my guess would be make the tap to apex points on the thread, then nick the tops off anyhow. Make the die / thread box so a small flat exists between threads (maybe a mm) - the tip of the screw has no strength and does no useful work.

I promise I will do another drawing soon as I get a minute...!!

here's a rough sketch minus the calcs for precise diameters and pitch

Thanks Hopper - let's try this... resized small in P'shop. Top pic is my custom tap 42mm 4tpi, second tap is a commercial 1" 6tpi that works very well, next pic is the shop-made thread box with ali outfeed and O1 vee cutter. Last pic is box at work into oiled beech. I'm working out the drawing but realised it isn't so simple, if I want small flats (or rads) at the apexes the geometry becomes a bit more complex - to me anyway... drawing soon

Hi Jimmy and Max - i need to draw it properly, will do that tomorow and send or attach here, I see a pic upload button now.
The thread form is not very critical but 60 degree seems good compromise as wood has grain of course and failure will tend to be along the grain. Also it's common to have a small flat on internal and external - the extreme tips of vee do nothing and on the male they just fall off anyway (wood again!)
Re material, a really nice option would be to case harden but all the ones I have used new and old have just been decent steel, not hardened. I'd need to mill flutes on along axis but I can do that (mate with a good milling m/c)
SO, sketch to follow - thanks all for the help, advice etc
Pics of the vices are here if interested:
**LINK**

Thanks Martin C - I can sketch this and take a pic, but how do I upload a pic? (do I need some min no of posts?). I have to start with 2 diameters (min and major) as I must buy Forstner bits in std sizes. According to what I have at the moment and some rough sums, I think a 35mm minor diameter and 45mm major may do it. So tap hole is 35mm, die blank (turned hardwood dowel) is 45mm.
I took a 4.6TPI as a guess of what would be good, my current is 4TPI but I think a tads finer would be good - in a vice obviously speed and clamping force are traded. So if 4.6tpi, then my reckoning is 9.77mm diameter difference at 60 degree vee form. I can get 35mm and 45mm, and grind a 45 down to about 44.7 so that would be easy.
I could sketch and put it on facebook pge if that helps??

That's it Martin, I am making a custom one of those. I have a 42mm 4tpi at the moment but the tap (which was kindly made for me) is on its last legs and the flutes were cut wrong. By making the tap and outfeed I have control over everything - diameter, pitch and accuracy of fit. On the current one I get really nice close-fitting screws and nuts, so I am looking to go the next step, a mandrel starter then tapered tap. The mandrel is important to start the thread dead on axis. The original tap[ was cut on an old Barnes, but I'm sure I can find someone up for the challenge ... haha.

Thanks - Hopper, wood components onto the lathe isn't an option - due to sizes, and the number I need to do, it's very slow and faffy. From my experience the tap and die is the way and you see old sets around (ebay etc) - it just works very well.
I was told by a mate I could do this on the Myford but I'm not a great metal worker and also the volume of steel to come out would take great patience I think, and put a fair load on the little ML7. I really need to pay someone with larger machinery to do this for me, I can then get on and make the vices !! Actually making the thread box is no small task, getting it dead right is a challenge (to me anyway) - i'd post a pic of a screw and nut but not sure I can post pics yet.

I need to find someone who can make a big custom thread tap for me. I have an ML7 but it's beyond that I think. It's approx 45mm major dia, and around 4 - 5 tpi. It's for cutting wood threads for some vices I make, the reason for flexibility in diameter and pitch is that from a new tap I then make a thread box to match (basically the die part) so I'd need a matching female thread into ali stock to make the outfeed for the die / thread box.
If anyone with a bigger lathe and v coarse pitch gearing will consider this I will pay of course - exact drawings etc will depend on pitch and then I need to check available Forstner bits to get minor and major diameters right - but I would provide a working drawing. Any help appreciated.

Took the plunge! Collected an ML7 last week, vintage 1953. A lot of signs it was cherished and it does seem very good so far. Also it had a large amount of bits with it, some of which I don't recognise yet but plenty I do: cutting and boring bits, vee blocks, sine bar, shims, chucks, knurling tool, various measuring tools etc

I was drawn to the Myford in the end as I think it will hold value, easy to get bits for it and only a little bigger than the ML10. And it is an interesting (and I am sure original) green-blue colour, hammer finish.

Need to get it installed and get some brass stock in!

Update: all good advice thanks, and I am trying not to do my usual - rush out and buy the first thing that I take a shine to. I missed a Myford ML10 close-by yesterday (sold an hour before). The Perris went yesterday at £220 - but Pete, points noted. 50 brass knobs hand-turned??!! I'd rather eat my own leg.

I plan to go and look at a C3, and keep my eye oout for anything good second-hand too. I can allow a small dedicated table / bench (on wheels) so don't want to rule out a Myford or other British older lathe, but I would like to find something local so I can view first.

Excellent advice, great forum, many thanks again.

Edited By douglas coates on 30/04/2012 06:32:38

Many thanks for all the help - it's hard to know where to start. I would really like an old Myford!, but I'm in Kent... Wirrall is a treck. I shall have a look though. I've seen an ML7 close-up and I like British engineering a lot.

One reason I considered the Unimat was the mill combo - for my very light occasional use I thought it may do everything in one small space? When I say up to 40mm dia, I mean occasionally, mainly smaller and brass of course, not steels.

The Peatol is the Taig I believe - haven't been able to find one yet. I am really thinking second-hand. In my experience with woodworking machines a lot of the newer 'affordable' stuff can be disappointing quality, and it may be true with this too?

I' have looked at the C3 but worth a trip to Axminster for me (close-by) to see a real one.

And there's a Perris PL100 on ebay - looks trad British again. Any good? (Off to find the ML10 now.

Hello, new here! I am a furniture maker but often need small components in non-ferrous metals - finials, feet, knobs etc.

I want to get a mini lathe and would like advice. Typical work will be under 40mm dia, mainly brass and similar alloys. I can live without thread cutting I think (resort to taps, dies) but occasional milling would be very handy too.

It will get light / occasional use but I do want precision - I am fussy!

A friend recommended the Emco Unimat with mill attachment - the Austrian-built SL or the no3 (says the 3 is better...?)

Any advice please - I dont want to spend a fortune but I know quality costs - is max £500 realistic (second-hand I am thinking).

Thanks for any help.