Reproducing a thread for a tool

Hello all

Would it be possible for a skilled machinist to make a hub puller tool that has an external thread, which then screws into the hub's internal thread, using only the hub's internal thread as a pattern for the tool?

Hope that makes sense... the problem is no one knows what the thread is but I have a spare hub that could be used as the pattern. ''it is only a hypothetical question at this stage''

Thanks in advance.

Simple answer is yes! but it would be helpful [not essential] if the male part was available to ascertain the thread form/angle. Also one would have to have a lathe of suitable size -- what's the O/D of the hub?

John, that is the problem, the male part isn't available, a tool did exist specifically for the job but unfortunately it's owner has lost it! From memory I'd estimate the diameter of the internal thread to be 40-50mm.

By using thread gauges ( either metric or imperial or both) it shoud be possible to define the the thread pitch . Making an impression of the thread with araldite ( apply penertrating oil before hand and allowing most of it to evaporate) it should be possible to double check the thread angle if you're not sure if its 55deg or 60deg.

Knowing these thread details any reasonably skilled turner can then turn a screwed shaft ( bolt) to fit the hub. It may be prudent to make the shaft out of high tensile steel (EN8 or better).

Knowing what the intended application is and the age of the tool would help in predicting the thread form.

Two possible methods - balsa wood of the approximate diameter can be screwed into the thread to leave an impression which can be checked with thread gauge or get some Fimo modelling 'putty', oil the thread and press the Fimo in to fill the cavity, remove and bake in the oven. The latter will give you a very strong, accurate form.

Rgds

Bill

silicon putty is available for that purpose in NDI

You could use "polymorph" for the same thing. It's available from Maplins.

Looks to be a potentially uaseful material for a number of things, as it's a thermoplastic that softens at hot water tempertures and when cool is as rigid as something like the hard polysytrene. I believe it is nylon based and can be (reputedly) machined, drilled and tapped in its cold state. I've wondered about work holding possibilities as well.

Keith

If information like country of origin, industry, rough manufacture date is available - it may well be possible to make some intelligent assumptions on likely thread series, then with pitch gauges and calipers identify the specific thread. Of course if the thread is a 'special' or a particularly unusual one then the methods mentioned by others above will come into their own.

It's a fairly well established technique, one type of plastic for workholding can be found here:

**LINK**

A UK source may be more practical in terms of shipping.

Regards,

Andrew

Terry, still not a problem the only reason for the male part was to asscertain the thread form and several other member's have suggested methods of obtaining this, you only need the thread angle, 60deg or 55deg etc. the rest is easy!

Where are you situated?

Hi Andrew

Looks like if polymorph isn't the same stuff exactly as as the "Soft Jaws" in your link, then it's a VERY close relative. From memory I paid about £12 for a 250gm tub. I think other places in the UK sell it as wel,l as I recall seeing it mentioned in some modelmaking magazines. Possibly available from hobby type suppliers as well as model shops.

Keith

How about trying hot melt glue from a glue gun to make an impression of the thread. I do not think it sticks very well to metal so a parting medium may not be required.

Les.

Good Lord Jim, are we allowed to use a candle in the workshop ? Or more importantly, does the dentist hold a dripping stick of this stuff over yer gob to tale an impression.

Well, firstly, thanks all for your help and suggestions, there are some good ideas which I can try.

Just to throw a bit more light on it, the hub is a propeller hub on a Gipsy Major aero engine, the origins of which I understand are French and again others have told me some of the threads on these engines are a metric form.

The frustrating thing about this is that there was a specific tool made for the job and the engineer who is associated with my Auster had one, but loaned it out, and it hasn't been seen since, It was a simple tool which on the face of it would be a fairly easy task for someone rather more competent than I to make, subject to being able to cut a mating thread.

I think my next move, will.... ''assuming the awol tool doesn't return'' be to make an impression of the thread from a detached hub using one or more of your method suggestions.

So thanks again I'll let you know what transpires.

According to my book, removal should not be required unless the engine is in for a complete overhaul. Can't give you the thread dimentions, but I'v got the D.H. part number T 800-54, and box spanner T 800-50 to screw it on, these are proberbly collectors items today. D.H. didn't specify the size of tools spanners etc., they just gave a part number, that way you got the spanner of the right length to give the correct torque, think it took the Americans to introduce the torque wrench.

My book is for the 120hp Gipsy III, and the last update is 10 / 10 / 34, like the tools, a collectors piece.

Ian S C

Ian, it must be a different front end on the 3, mine is a 10-1-1 and removal of the hub is required in order to replace the crankcase front cover.

Terry

Terry, just back from wandering around google, theres not a lot on Gipsy Majors is there.

You could try contacting the Croydon Aircraft Co Ltd, in New Zealand. They mainly rebuild, and over haul D.H. aircraft, but also other vintage machines, wood and rag the speciality.

www.croydonaircraft.com/CAC.html

These blokes know Gipsy Majors.

I imagine your Auster has a metal prop. Ian S C