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View Full Version : Leadscrew and matching nut machining - Evan



snowman
03-03-2008, 09:04 PM
Hey Evan...

Are you willing to go into a little detail on the manufacturing of your leadscrew and matching nut?

Evan
03-04-2008, 08:36 AM
There isn't that much to tell. I made a tap from some of the leadscrew stock. It's nothing special and not hardened, no special treatment and no special expensive grinding wheels either. I actually cut the flutes with an angle grinder and a guide that I mounted above the tap in a vise. An acme tap has a lot of material to remove so it should have a very long lead-in compared to a regular tap. Since the tap and the lead screw are the same size it doesn't produce any clearance. That's alright with acetal but if you tap brass or bronze the required clearance can be had by freezing the nut after the first run through and running the tap through again.

Here are the tap, an acetal nut in it's holder and a bronze nut made with the tap.

http://vts.bc.ca/pics/lsnut1.jpg

http://vts.bc.ca/pics/lsnut2.jpg

Don't try to power tap acetal. It will melt and spoil the job. Do it by hand and it will be no problem. Oil can be used as an aid for tapping acetal.

PS: My internet has been down since yesterday thanks to the mother of all snow storms that dumped over 3 feet of snow on some areas around here. Heavy weather disrupts satellite internet.

Mcgyver
03-04-2008, 08:48 AM
nice job Evan, I like the freezing trick. are you starting from a hardened ground screw? just wondering how hard it was as it obviously had no trouble with the bronze

KiloBravo
03-04-2008, 08:55 AM
I made a tap from some of the leadscrew stock. It's nothing special and not hardened, no special treatment and no special expensive grinding wheels either.

Mcgyver, I can answer that one :)

Evan
03-04-2008, 08:59 AM
The stock is 4140 I seem to recall but not hardened. It turns like about half hard or normalized (not annealed) steel.

Mcgyver
03-04-2008, 09:12 AM
Mcgyver, I can answer that one :)


Awe geez, I'm just getting over the flu and figured i had about 30% capacity restored. guess its more like 5% and i better stay off the boards for a few more days :D

Evan
03-04-2008, 09:27 AM
I forgot to mention that the leadscrews are rolled, not ground. That alone will raise the hardness a lot because of work hardening.

snowman
03-04-2008, 06:13 PM
thanks Evan. I actually found your initial post describing it after posting this and forgot to update my ignorance.

Do you feel like you really did a great job on the tap geometry, or is it just roughed out? (I figure if you feel it's roughed out, I might actually be able to do it, you are a tad more meticulous than I)

Evan
03-04-2008, 08:55 PM
Not a great job. The first attempt wouldn't cut hardly at all. It didn't have enough relief behind the cutting edges. It took a lot of patient and careful hand grinding to bring the back relief to within a few thou of each of the cutting teeth. That plus having some positive rake to the cutting edge is really all that matters. To achieve positive rake the cutting edges must be undercut when the flutes are ground. You must also be sure to grind the flutes deeper than the root of the threads by about twice the crest to root depth. That gives the chips somewhere to build up. I used three flutes but two will do as well and makes for easier grinding but a harder to turn tap.