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motorworks
08-03-2004, 07:26 PM
Hi
I have to cut a 5/8-8 internal acme thread approx 3" long.
Bored out to TDS tonite,but I do not have a boring bar (ie internal threading tool) small enough to fit in the hole.
I was going to grind one out of a 3/8 allen key.(well two, one vee and finishing tool).
But I said I would go home and get some suggestions first.
Well, what you guys think?

wierdscience
08-03-2004, 07:32 PM
Damn shame Motor,I got two sets of 5/8-8 acme taps,right and left http://bbs.homeshopmachinist.net//tongue.gif

Maybe a section of drill rod with the end turned to the profile,heatreated and ground.

If its soft the allen wrench might work.Why is there 3" of thread?

John Stevenson
08-03-2004, 07:39 PM
If it was me I'd tap it but then again I have a tap that size.

Sorry couldn't resist.

Seriously holding a tool thru a bore this small over 3" won't be easy.

Two ways.
I would be tempted to make a boring bar up the exact same diameter as the bore and use a piece of broken centre drill as a tool.
Keep the boring bar at the same setting all the while and advance to tool by pushing with a small grub screw from the back.
Drawback to this is you have to remove the tool before winding back but the thread has to remain parallel as it's supported by the back of the bore.

Next method is to make a tap out of drill rod and screwcut a rough thread first then tap to finish

motorworks
08-03-2004, 07:48 PM
Thanks guys
Nut is for a friend who is making a motorcycle jack.He asked for it to be 3" long.
I have an on going search on ebay for acme taps,but no luck yet.
Love to have a set of 5/8-8 LH and RH or a "friend" near by with one!!
Oh well.

mendoje
08-03-2004, 10:03 PM
Could you make a tap, or a threading insert, using a length or chunk of the 5/8-8 threaded acme rod?
Jeff

lenord
08-03-2004, 10:11 PM
I'd make a tap out of a piece of the corect size acme rod myself.

FWIW
Lenord

wierdscience
08-04-2004, 08:16 AM
Ask him if you could counterbore the part so the thread only amounts to the first 1-1/2"

G.A. Ewen
08-04-2004, 08:24 AM
Another possibility would be to use 3/4" ready rod and a connecting nut.

SGW
08-04-2004, 08:34 AM
Revisit the need for it to be 3" long. You certainly don't need that much for strength.
1" ought to be plenty.

coles-webb
08-04-2004, 07:55 PM
If you are going to cut the male portion of the ACME thread then I would do as some have suggested and make a tap, both a roughing and a finishing. I have made many tools out of drill rod,4130 or tool steel and heat treated with a torch. It is a great learning experience and the tooling will get used somewhere else. See the attached photo, the cutter on the right is a3/4 inch radius cutter made with a 303 CRES shank welded to a tool steel cutting edge. I heat treated with a torch and have cleaned up the cutting edge with a flapper wheel. I made it to make a new part for a 4 inch mill vise that cracked. It has been used to machine 4130, hot rolled steel and aluminum.

http://www3.sympatico.ca/mike.coles/cutter.jpg

Mike

motorworks
08-04-2004, 09:07 PM
The owner picked up some nuts today.
Thanks again, but I am going to make the tap as a project in my spare time,both a right and left hand.Any tips ?
take care
eddie

John Stevenson
08-05-2004, 04:38 AM
Eddy,
I made mine by taking an old Myford leadscrew and usng the unworn portion at one end, milling some flutes and back relief and having it cyanide hardened.

It has served me very well to say it's only mild steel.
I have tapped quite a few nuts with it and since I have had the electronic gear hobber it's now serving as a hob to do worm wheels.

http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/acme.jpg

So far I think we are up to about 40 worm wheels with this as a cutter.

If you don't want to go this method with a lengh of pre bought in acme all-thread then it's just a simple turning and screwcutting exercise.

The purist's will ooo and haa about lack of back relief but unless you are doing 1,000's in tool steel these will cut and go a good job.
I have made many specials over the years just out of silver steel [ drill rod ] and hardened and tempered with a torch.

I usually cut three or 4 flutes in depending on the size of tap, the idea is to only have a smallish land of threads to reduce rubbing.
I also mill these slots in by eye and don't bother to index round, it's best if they are slightly out and then it reduces the cogging effect where it tries to generate a 3 or 4 cornered hole as it moves from flute to flute.

HTH

John S.

[This message has been edited by John Stevenson (edited 08-05-2004).]