Author Topic: Screws custom made?  (Read 5377 times)

Offline Shotgunlover

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Screws custom made?
« on: October 23, 2011, 12:53:07 PM »
Hello all,

I have been trying to get some simple, or at least they seem simple to me,  ALUMINUM screws made and have been given the run around by manufacturers. Maybe someone here has some ideas to get out of the impasse.

Let me describe the "project": a push type knurled thumb screw, total length 1 7/8 inch, threaded length 1 1/2 inch, thread size 5/16 27 tpi. I know this is an uncommon size thread. Two manufacturers that tried, gave samples that did not fit the intended receptacle.

Knurled aluminum thumb nuts to fit the above were part of the deal.

So the plan was changed, to a more common thread size, same length but tread 8-32. Still no joy. Some gave lead times of 10 weeks and costs that are through the roof.

Anyone have any ideas about how to find a source or maker of such screws? The only strict requirement is as to the material, aluminum being choice No 1 and brass a second alternative.

All the best

Shotgunlover

Offline Lew_Merrick_PE

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Re: Screws custom made?
« Reply #1 on: October 23, 2011, 02:17:39 PM »
Shotgunlover -- (1) Can you get a hard wax or Muntz metal "master" of the (5/16-27) internal thread you are trying to match?  That would give whomever is making the "mate" the ability to get a measurement over wires to assure fit.  (2) Are you sure that these are 60° threads rather than (Whitworth) 55° threads?  (3) How many of these beasties do you need?  That determines many things.  (4) If you can go from a 5/16 major diameter (ø.3125) to a #8 (ø.1640) major diameter, there is probably a lot of wiggle room in the design (or did you mean 5/32 which is ø.15625?).

The thing about custom threads is that defining them is less trivial than generally thought.  If a lathe operator is making one external thread to fit a supplied internal thread, then all they really need to know is: tight fit, snug fit, or loose fit.  Developing measurements and gauges to qualify parts made across distance and time is one of the major exercises in the screw/nut/bolt manufacturing world.  People forget that even Go/No-Go gauges have tolerances (something that caused me several weeks of work to demonstrate back in the late-1980's).  Until you can really define it, your problem is not going to be solved!

Have you thought about purchasing (say) brass socket head cap screws (not uncommon in the maritime trades) and then merely making a press/solder thumb-cap and thumb-nut for them?  (Let me qualify this by saying that I am aware of brass SHCS's, but I have never purchased them myself.)

Offline Jasonb

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Re: Screws custom made?
« Reply #2 on: October 23, 2011, 03:26:27 PM »
How are you measuring that thread as 5/16" x 27 GAS actually has a major dia of 0.342" not 0.312, that may be why things are not fitting!!

J

Offline Jonny

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Re: Screws custom made?
« Reply #3 on: October 23, 2011, 07:09:47 PM »
Wouldnt it be easier and work out cheaper to go for a standard well used thread such as M8 X 1.25 or even M8 X 1. Ok if the thread in the adjuster is made to suit.

Is this for looks or purpose?
No torque on hand tight stuff especially with that recoil.

Have done several ways think of aluminium T with cap head screw counterbored in the exposed raised knurled.
Also done in stainless and aluminium 6082 one piece with lever.

Over here we have Maplins they do thumb screws in aluminium but will be metric, one person pulls a fastun and just mill indexes cutouts through the anodising complete with burrs :clap:

Offline Shotgunlover

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Re: Screws custom made?
« Reply #4 on: October 27, 2011, 05:55:23 AM »
Thanks for the replies.

The fit is loose, since it is a non critical application. The parts are simply hand tightened.

I have now started making epoxy-powdered steel casts from the female threads to have a precise  sample for future reference.

The quantity for the above is minimum 500 max 1000.