Help Please - screwthread ideas

Hi all,

A couple of us want to build an actuator for a large (3m) satellite dish. It only needs to wind it up and down in elevation, and will be fairly well balanced. We intend to make a screwjack arm to push it up, but are unsure what will be the best thread type to use. I have seen elsewhere a thread which I can only describe as square - it is about 0.5inch pitch, and the thread looks totally square in cross-section, I guess for good load-bearing capabilities.

My questions are:

What is this thread called (if you can identify it from that poor description!)

Is it the best profile to use, or should I be looking at something else?

Where are some good places to get 1.5m from, along with the captive nuts etc?

Thanks

Gary

Reply to
Gary Cavie
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Gary The ideal thread to use would be Acme as used for zero backlash drives on machine tools; it's almost square in section, I guess that's what you have seen. Sorry, no ideas where to buy such a large size (it will need to be large for a 3m dish) unless you know anyone who breaks graphics art equipment, as I know several filmsetters (photo typesetters) that use a long and very heavy duty leadscrew that would probably be ideal. Martin.

Reply to
Martin Whybrow

Try:-

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You are looking for Acme or Trapezoid form.

-- Regards,

John Stevenson Nottingham, England.

Reply to
John Stevenson

Terrible waste - those are PRECISION (and then some) leadscrews.

BugBear

Reply to
bugbear

from John Stevenson contains these words:

John, I hate to but-in to even suggest that you might be mistaken (I've been taking this NG for about 2 months and the quality of your advice has never been in question [forgetting the resident Troll]) but I do know a little about threads - I used to work for Herbert Small Tools and anything to do with threading was my responsibility. The thread described by Gary is undoubtedly a Square Thread - a BIG B****r but a square thread non-the-less.

I would absolutely agree that what he really needs is an ACME 29 degree form or the metric equivalent Trapizoidal 30 degree form, and a 1.5M length at probably 50mm OD isn't going to be cheap! - A Square Thread form would probably be 50% more expensive to manufacture and would be weaker.

JG

JG

Reply to
JG

I know, the maximum short term error on these is around 2um and about 200um over the entire length. It sounds wasteful to use one of these for Gary's application, but these machines do get scrapped and these parts eventually get turned into tin cans rather than put to some good use. Martin.

Reply to
Martin Whybrow

If the elevation angle is critical to you it may be that a square thread will give you too coarse a pitch to accurately position the antenna. If the dish is well balanced the load factor may not be that high and a fine thread form could be suitable.

Reply to
Alan Marshall

In the US, roll formed Acme threaded stock is available from the large

machine shop supply companies and from fastener suppliers that cater t the larger side of things. It is not high precision with 0.005 t

0.010 inch per foot pitch tolerances. Generally available up to abou 2-1/2 inch diameter. Two inch diameter with either 4 or 5 threads pe inch is about US$100 for a six foot lenght. Matching nuts are abou US$15 to 20 each in this size. I know this does not help you directly but it may give you some general price guide lines and an idea as wher to look

-- GailInN

First R/C 1956

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Reply to
GailInNM

Try Acrow Props. They hace a nice 2" diameter square thread. Don't know what lengths they come in though. You might weld a couple together....

Dave

Reply to
speedy

[snip] The thread

Well, Acrow Props are certainly not weak! They are in 2" tube and have a square thread form. The cast "nuts" are pretty hefty things too, though maybe not high precision.I shouldn't imagine that they are expensive.

Dave.

Reply to
speedy

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