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Threading DOM on a lathe

1.9K views 13 replies 5 participants last post by  86lxnotch  
#1 ·
Anyone ever use a TAP in their lathe to tap Dom? I find it a pain to center/square the tap to the DOM by hand and figured using a lathe would work better. Not exactly sure how to proceed in doing this other than just using the lathe to hold the DOM and TAP and turning the chuck by hand to get it started??

Any thoughts?
 
#2 ·
First you need to make sure the Internal diameter is what the tap size you are using calls out for. You can find the major/minor diameter in a Machinist handbook, or probably on the internet. Depending how accurate you want your tapped hole to be, indicate your peice in(4 jaw). Your best bet would have as little stock sticking out. Lowest RPM in low range. Lube the heck out of the tap and inside the tube and continue when its tapping. With your tailstock free, gently feed the tap in. If the tap catches and spins, kill the lathe, tighten the tap up, relube and start it up again. You can reverse the chuck and back the tap out to free any chips, but I wouldnt suggest taking the whole tap out because it can be a pain restarting it. When you are backing out, help the tap by gently pulling the tailsock back. Again, dont have the tailstock locked down, it should be free moving on the ways. I like to put a little chamfer on holes I am tapping. It gives it a nicer appearance and tends to be a little easier to start because your protecting the first initial thread from getting banged up.(do the chamfer before tapping)

Very simple. once you get bored with it, try internal threading!
 
#4 ·
Starting the tap on the DOM tubing can be a challenge to get it straight, I've done it by hand with success and some fails so this time I'm going to use a Lathe to get it squared on.

In stall the DOM in the chuck with only about a 1/4 sticking out the front of the chuck.
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If you can bevel the inside edge about 30 degrees, this will help the TAP start off straight.
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The tap has a center punch for a tail stock.
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Using the tail stock to center the TAP on the DOM
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Using a wrench and with the chuck of the lathe brake on start threading the tap into the DOM, while your turning the wrench continue to feed the stock to keep pressure on the tap.
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About 3/4" in.
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Threads are looking good and even all around, the tap is going in straight.
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#7 ·
It looks like the whole lathe is brand new, so that 3 jaw should be holding a pretty tight tolerance, maybe .003" which is the thickness of notebook paper. Assuming these are for heim or johnny joints, that .003" isnt going to affect anything, especially if its the "factory" bore. 7/8" should give you no problems with catching. Clamp the tap on the round part so if it does decide to slip, you wont break your tap. Just lube and continue lubing!

Has the lathe been leveled and tailstock indicated?
 
#8 ·
wow thats WAY more work than needed. i set the DOM up the same way in the lathe itself, 3 or 4 jaw never mattered for me. on the tail stock i toss in a countersink and dig it in about 1/8-3/16'' and then put the tap in a 4 jaw drill chuck. low speed, lube it up and go to town. never had a issue that way. the majority i did like this was 1'' .156 wall which is a 3/4'' NF tap
 
#11 ·
Maybe, but this way I know it was perfect center. I used the lathe to power feed the tap down in once I had it started. I just through in a drill chuck into the tail stock to hold the tap and set the lathe at 70rpm.