First Try at Metric Threading

[erikmannie]

I have done a bit of Imperial threading, but I will be doing a lot of metric threading now (for fun!).

I started out with 1” steel hex, wanting to do M16-2.0. I overshot the diameter because I was confused about how to read an analog metric micrometer. So on to M14-2.0, then.

I left the half nut engaged throughout the whole operation. This is also the first time that I have had my DRO on mm.

I won’t be able to get a nut to test it for about 6 hours.

Here are some pictures in case anybody has any constructive criticism, particularly with regard to the compound being set at the correct angle. I see some chatter.

 

[erikmannie]

When I left the half nut engaged the whole time, I disengaged the power lever upon arriving at my safety groove. I then backed out on the cross slide, and then used the power lever to rotate the chuck in reverse which moved the carriage back out to get ready for another pass.

 

[benmychree]

I think I see a built up chip edge on the tool, that will effect finish quality, what cutting fluid are you using? The way the chips are turning black, I'm thinking perhaps too much speed, which would also tent to cause chip welding on the cutting edge. A little undersize on the major diameter is generally not a problem; the OD of a thread is usually filed off to eliminate burrs, so the OD usually ends up under the nominal size anyway.
A 3 jaw chuck is much better than a 4 jaw for holding hex stock accurately centered with much less fiddling around.

 

[Aukai]

Learned a bunch, thanks for posting....

 

[erikmannie]

I think I see a built up chip edge on the tool, that will effect finish quality, what cutting fluid are you using? The way the chips are turning black, I'm thinking perhaps too much speed, which would also tent to cause chip welding on the cutting edge. A little undersize on the major diameter is generally not a problem; the OD of a thread is usually filed off to eliminate burrs, so the OD usually ends up under the nominal size anyway.
A 3 jaw chuck is much better than a 4 jaw for holding hex stock accurately centered with much less fiddling around.

My CF is 70% Mobilmet 766 (Neat Cutting Fluid, an oil) and 30% Mobil DTE 24 (light hydraulic oil).

The RPM was about 70 to 100 RPM.

I never mind fiddling with a 4J chuck, but I will put the 8” 3J on there because I will be doing this for the next 7 days.

Thank you for the help. I did not notice the build up on the HSS threading blade, but I see it now.

 

[erikmannie]

Question: why don’t people with inch pitch leadscrews leave the half nut engaged throughout the whole operation for Imperial threading as well, as we do with metric threading? It is no trouble at all, and there is no worry about missing the mark on the thread dial. It would coast the same distance if I used the E-stop button.

Second question: I’m curious to see what is going to happen when I try a much smaller safety groove and stop the threading pass with my foot brake. When I disengage my power lever to stop power, it coasts for about 8 mm as the chuck is spinning down.

 

[Ischgl99]

Looks good! Most of what I do is metric. I don’t mind keeping the half nuts engaged and reversing, it doesn’t seem any slower than using the threading dials once you get some practice.

What kind of threading tool is that? I already bought an Arthur Warner on edge holder, but that looks interesting.

 

[Ischgl99]

Are you running a VFD on your lathe? If so, check your deceleration time and shorten it stop quicker.

 

[mikey]

Erik, you're developing some tearing on the trailing edges of the threads. This might have to do with how the Aloris blade is ground; you may be at the limits of the helix angle that tool will allow. You might also check to see if the blade is level/horizontal; the bolts have some play so check to see if it is level.

The other thing is that your thread relief is a bit too shallow. When the tool runs off into that thread relief there should be no contact of the tool with the work. Typically, the depth of the thread relief is 0.003-0.005" deeper than the minor diameter of the thread. This will not affect the strength of the work piece.

 

[benmychree]

For threading, I use TapMagic, it will give you a better finish, and yes, the tool should be adjusted in the holder to approximate the helix angle of the thread being cut and ground parallel with the axis of the lathe on top; this does not mean that you need to adjust for every different pitch that you cut, one grind will work on nearly every thread that you cut. I have used those Aloris threading tools since back in the 1970s and really like them, they also come in common acme thread pitches. Note that the Aloris tools and tool holders are made so that they can be inverted in the holder and used to thread with the work rotating backwards and feeding from left to right for RH threads.