How to cut internal Acme threads in a finished piece?

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tetrode

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Hi, All. This is my very first post to this forum so please be gentle :)

I'm not a machinist (yet) but really do need to pick up some basic skills. I often have the need to fabricate small, non-complex pieces for prototyping designs I've come up with. Here is my problem du jour:

I need to have 3/4" x 5 Acme threads cut into the mounting socket on a piece very much like this one:

Umbrella_Swivel_Acme.jpg


Depth of the socket is approximately 1-1/8". Material is cast aluminum.

I know Acme taps are available (at a steep price) but what I don't know is if an Acme thread of the required size can be tapped by hand or if a mill (or other piece of machinery) would be required to do the job. So here's my basic question: Is this a DIY task for the non-mill owning person or something better farmed out to a machine shop (assuming one could be found equipped and willing to do the job)?

Any guidance from you forum experts would be greatly appreciated.

Thanks in advance.

Dave F.

Umbrella_Swivel_Acme.jpg
 
I don't know about that size but the 1/2-10 acme tap I bought is not hard to do by hand. It has two thread sections that go through successively.

I paid around $60 for mine and although it is a low use item and expensive, it doesn't take many uses to make your money back.
 
3/4-5 ACME is one of the more rare varieties and not many folks will have that tap around. Cast AL is not going to be easy to tap either...

If you were a customer, I try to see if there's some other convenient adapter that could serve your purposes. Such as a stud that fits inside the fixture but, has a female ACME receptacle on the other end etc...

Ray

EDIT: To answer the other part of your question... BTW: I've done inside and outside ACME threads on a lathe. Big surface, lots of pressure... This is a job for a lathe or CNC mill.
 
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Thank you both for your speedy replies. The object of this exercise is to determine if photographic grip accessories with standard 5/8" "baby" pin receptors can be successfully modified with internal Acme threads so that they can also be attached directly to standard painter's poles which all have the 3/4-5 (nominally) Acme thread. Currently, an intermediate adapter is required. This is the business end of a typical painter's pole:

Painters_Pole_Acme_Thread.jpg

Painter's poles provide a very economical and portable way to elevate lights when working on location and with an assistant.

I should also point out that a two-stage roughing and finishing tap won't work in this application because it's a blind rather than through hole I'd be working with. Would that mean two separate 3/4-5 taps would be required? UGH! The least expensive Acme tap I've found in the size I need runs approximately $160.

Painters_Pole_Acme_Thread.jpg
 
3/4"-5 Acme is the thread found on most broom and paint roller handles. I have seen taps for it but like said they are a little pricey.

Is the hole you need threaded thru or blind?


Edit, I see tetrode responded while I was typing and answered my question.
 
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It looks like your cutting into aluminum you can make your own acme tap for this and it is not as hard as you may think I have made a few and they work well.. Ray
 
iron man said:
It looks like your cutting into aluminum you can make your own acme tap for this and it is not as hard as you may think I have made a few and they work well.. Ray
Click to expand...

I've watched a few youtube videos demonstrating how to make your own Acme tap using a length of Acme threaded rod, a Dremel with a supply of cutting disks, and a *very* steady hand. I'd be willing to give this a try BUT 3/4-5 Acme threaded rod (when you can find it) is fearfully expensive. For example, a 3' length from mscdirect is over $72:

http://www.mscdirect.com/browse/?navid=12101927+4288179921

3/4-6 is, apparently, a MUCH more common size and is readily available on eBay for quasi-reasonable prices.

EDIT: I should add that Tracy Tools in the UK has the 3/4-5 tap listed on their site at a very reasonable price. Unfortunately, there is no stock:

http://www.tracytools.com/taps-and-dies/acme-taps?product_id=470
 
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For ACME rod, try a fastener fabrication place (I use Brafasco), as you may be able to get it cheaper. I use a lot of 1/2 ACME rod and even did once buy a chunk of 3/4 (3 ft sounds right) but the price was only about $40.00 (the 1/2 costs me about $30.00). I use a tap to cut 1/2 ACME threads and its not hard by hand (and Im talking steel, not aluminum). Just have to take your time.
 
Stupid question, but couldn't you just use a belt sander or a file and make the end of the broom into a 5/8 peg? Or would that defeat the purpose? Figure a $9 file or $ 5 sanding belt and some time is a lot better than $60-$90 for a tap that won't get used often. That is if you don't have access to a lathe. Or even easier drill and tap the end of what's there to take a 5/8 stud. That can be done with a hand drill and a $4 tap and die and some cheap metal bar stock.
 
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