Butress Threads

I need info on cutting butress threads. Tool geometry, possible problems, how to measure. These will be cut on a manual lathe. Male and female threads. Thanks.

We could write you long winded replies but it's actually best to refer you to Machinery's Handbook where there are a couple of pages on the subject of buttress threads with illustrations.

Buttress threads tend to be coarser than V threads or even Acme. There's a lot of material to come out of the thread space and for that reason I reccommed a follow rest be used if the thread you're cutting has any length to it.

Otherwise use sharp tools on the final cuts with plenty of oil. A material that machines nicely helps as does orienting the pressure flank correctly.

As for gaging the thread I suggest selecting a single wire (or drill shank) using calclulated data based on "Machinery's Handbook" formulae. If the external thread you're making is inconveniently long to use as a gage, make the product thread then make a short gage to the same settings to use in making the nut.

[ 06-21-2005, 07:50 AM: Message edited by: Forrest Addy ]

"possible problems"

yes, I know one good one.

this is a left hand 1-3/4" 8 tpi butress nut, I made 16 male parts and 17 nuts, I screwed up on this one.

the butress thread is directional and I put the hex on the wrong side of the nut.

I was lucky it was olny plastic and threads like a dream.

well there is one tip for you, good luck.

Yes, machinery's handbook has all the info. I once cut a 3tpi buttress thread for a press brake adjuster screw and nut in 4140 HT and alumium bronze. It was a short rod, but nonetheless not fun. It took many many light cuts at low speed to try to avoid chatter, even though it was done in a very large and rigid lathe. The really fun part was hobbing the worm wheel on the outside of the nut with a homemade setup on a Bridgeport.

I've cut a good number of male and female buttress threads. All hydraulic cylinder parts. Takes some practice....Forrest is right as usual.

I have a drawing somewhere of how to set them up and cut them. If I find it, I could snail mail it to you....

Andy Pullen

Tattoomike68...I feel better now...I'm not the only one who put the threads wrong.. I did it on a breech block ..What was I thinking...
Robbie

Amen Robbie , if you dont screw up sometimes you ain't doing much work.

realy I put the threads right I just milled the hex wrong, lol (same damn thing).

I am glad I still have that nut, it works as a reminder to me.

Look carefully at the specs for the buttress thread form.

First, grind your tool with the widest flat at the root of the thread as you can get away with.

Flat at root is in relation to pitch, the coarser the pitch the wider the flat. Don't wait for your pointy little tool bit to break while you have a cut going.

The last ones that I cut allowed 5 degrees of angle on the side opposite the 45, in other words the thread form was really 50 degrees included angle.

This is very nice. The tool is a wee bit fatter and thread cutting goes much easier because of the wider open form and the fact that holding 90 degrees normal to the shaft axis is, let us say, frought with difficulties.

I hope you have the nut if you are cutting the bolt or the bolt if you are cutting the nut.

Yes, I believe Machinery's hand book like the bible that it is, but measuring any thread by the three wire method is a task for which a machinist will have to consult his list of handy expletives.

The easy way is to buy topping inserts. I have made topping tools for rush jobs from a piece of high speed steel on our wire edm. The formulas in Machinery's Handbook make it easy.

hello there..i need some info on buttress thread..the standards are 5/45, 7/45 also few with 30 deg(googled it)..i wanted to know if we can have a negative degree for a buttress thread..like for ex: -5/45 ?? If yes, then how can we machine it..??

I can see this is an "archive" thread but I came up with this a couple of years ago re measuring pitch diameter on external and internal Buttress threads.

Proved popular especially within the aerospace industry.

http://f-m-s.dk/Buttress Thread Measurement.pdf

The latest is also measuring the minor diameter on an external thread and the major diameter on an internal thread.

Spamming? Maybe but only if you don't want to try doing it yourself.