I never knew there was a difference between an external and a internal acme tool. I cut the external with an insert I had the internal was a hss cutter I sharpened to fit my starrett no 284 screw thread gauge it's a no 4 acme .250 pitch two lead thread. And I'm using .143 wires. How do you like my method of holding the wires?
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Double Lead Left Hand Acme
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Tony,
On your Gagemaker sheet, if you watch the external root width for a given pitch, in respect to change in diameter, it will get wider. Your internal thread root width will not change. Also some of the Gagemaker programs, it will take in account multiple start threads in calculating MOW or set dimensions for rolls. Using pins no effect, but I don't like using pins on Gagemaker instruments. It doesn't give you an average as using rolls will. I have a nice spread sheet that I use frequently for vee, Acme, Stub Acme threads if anyone is interested in a copy. Infact, if I can upload it here I will. One thing I have to mention, it is only set up for class 2 vee threads and class 2G Acme and Stub Acme threads. Ken
On your Gagemaker sheet, if you watch the external root width for a given pitch, in respect to change in diameter, it will get wider. Your internal thread root width will not change. Also some of the Gagemaker programs, it will take in account multiple start threads in calculating MOW or set dimensions for rolls. Using pins no effect, but I don't like using pins on Gagemaker instruments. It doesn't give you an average as using rolls will. I have a nice spread sheet that I use frequently for vee, Acme, Stub Acme threads if anyone is interested in a copy. Infact, if I can upload it here I will. One thing I have to mention, it is only set up for class 2 vee threads and class 2G Acme and Stub Acme threads. Ken
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in an older edition of the machinery handbook (19 edition I think ) there is a single wire method for measuring acme threads. it tells you how to size the wire and use a straight edge to check the size. also you can use a gear pitch gauge to check the pitch circle by setting the gauge to the pitch circle and measuring the thickness on the thread at the correct depth, these are easy to do and give you correct size acme threads. bill
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- Dec 27, 2014
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here is something similar but on the other extreme, with a different approach to cutting the second thread.
These are a hob and a worm. They are 1/2" dia, 2 start, .125" pitch (.25" lead) LH thread. The cutter angle is 79 degrees included for a pressure angle somewhere between 10 and 14 degrees. The hob is O1 tool steel and the worm is 932 bronze. The hob was a total nightmare to cut, cutting deep into a 0.500" piece of steel does not leave enough material to prevent a lot of flexing of the part.
Since I am not burdened with a metric lathe, I simply half-nutted the second thread and cut both threads at the same time in the same set up.
If you have an imperial lathe with a threading dial with an even TPI leads screw, you can half nut quite easily. You simply close the half nut halfway or 1/4 the way between marks. My lathe has an 8 TPI lead screw, and this was cut at 4 TPI, I can close the half nut on any mark or half way between any mark. Cutting the second thread requires me to close the half nut either 1/4 or 3/4 of the way between marks. I am pretty certain the same trick will work on a metric lathe with an even pitch lead screw provided you have a threading dial.
Another very easy way to cut the second thread is to use a 4jaw chuck to hold the dead center, and simply drive the dog off opposite jaws. You can cut 4 start threads this way, or use a 3jaw to cut a 3 start thread.
The hob and worm a slightly different, the hob is a few thousandths larger in diameter (deeper cut into the wheel), and the thread depth a few thousandths shallower (shorter tooth height in the wheel) to allow clearances in the worm wheel. After I finished the hob, I slightly narrowed the tool so it would cut slightly deeper into the worm. When I finish the project (someday...), I will post a build thread on it.
-Josh
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I just finished cutting a two start 2" diameter acme screw with 1" lead for the clutch engaging part for a steam donkey at Sturgeon's (saw) mill near Graton Ca. (google it) The screw pushes the winch drum over into a wood block cone clutch; I still have to machine some castings including the one with the nut-to-be; all this is the better part of 100 lbs of castings, for which I made the patterns, also for two bearing caps for the winch drum, about 60 lbs each plus babbit. This donkey, or "road engine" was made to drag logs on a skid road from forest to sawmill, the pulling drum had over one mile of 1 - 1/2" wire rope on it; the haul back drum is empty, but would have about the same length of smaller wire rope on it. To achieve the 1" lead on my 19" Regal Leblond, I had to use change gears to double the ratio to the lead screw.
I use the half nut method to do the threading, as you can get the whole job done in one shot, cutting the alternate leads in turn,
Sturgeon's Mill is a historical preservation project, a non-profit that is entirely managed and done by volunteer labor; we run the mill four times a year for the public and cut logs that are donated where the had to be removed for safety concerns. We cut mostly redwood and some fir. The mill is entirely run by steam, having a 30 HP main engine that runs the 60" circular saw, plus top saw, and two smaller engines that run the four saw edger and trim saw.
I use the half nut method to do the threading, as you can get the whole job done in one shot, cutting the alternate leads in turn,
Sturgeon's Mill is a historical preservation project, a non-profit that is entirely managed and done by volunteer labor; we run the mill four times a year for the public and cut logs that are donated where the had to be removed for safety concerns. We cut mostly redwood and some fir. The mill is entirely run by steam, having a 30 HP main engine that runs the 60" circular saw, plus top saw, and two smaller engines that run the four saw edger and trim saw.