PM 1340 Feed Rates

The left hand letter gear selector sets the gear set range, the right one is the fine adjustment within that letter range. So 8 being the slowest and 1 being the fastest within that range (corresponding to the TPI). So E1 (64 TPI) feeds at ~0.005 IPR, E8 feeds at ~0.0027 IPR, so E4 would be ~ 0.004 IPR, E7 would be ~0.003 IPR. Cross feed would be 1/2 the carriage feed. On the D range, everything is doubled, and for each successive letter range. Pretty much for feeding you pretty much using an IPR range of 0.0027-0.010 (typically 0.008 probably for this size machine except with softer materials), so the Range of E8-E1, and D8-D1.

Thanks Mark, nice to hear from you. I thought that was the case but wanted to make sure. I really love the proximity stop you built for me. I have been practicing threading with it after watching your video. I'm starting to get the feel of this machine. Thanks again for all your help.
 
In the past many lathe manufacturers used a cross feed lead screw 1/2 the pitch of the longitudinal feed screw,
Therefore a .005 inch per revolution feed in the Z axis results in a .005 inch feed per revolution.

The X axis (Diameter axis) moves at 1/2 the feed rate for obvious reasons.
 
Cross feed is 1/2 the carriage feed rate per top of the feed diagram 1/2 cross feed to 1/1 feed. So 0.004" feed would be 0.002" cross feed. This is pretty typical for most the lathes I have seen, it is also indicated in the front of the 1340GT manual (see below). Most of you cutting feed rates will be in the E1-8 and maybe D6-8 (~0.008-0.003) for this size lathe, the rest of the gearing is primarily for threading. The ratios probably have more to do with threading increments. On this lathe the deepest I typically went in a DOC was around 0.1" (diameter of up to 0.2" in softer materials), steel was typically 0.1" for removal). It all depends on the material and the tooling you are using. (looks like the picture links are broken)

Thanks Dr. Mark!

I have had my 1340GT for nine months and guessed it might be something like that. I was disappointed that there wasn’t a feed table in the manual that showed the actual rate at each setting. I searched and searched on the internet but couldn’t find anything. I also have not been able to get Matt on the phone for months. No one else at PM really knows these details so I just gave up. I can’t remember if I e-mailed my question, but I guess Matt is just too busy to answer technical questions anymore.

I think I could make a chart for feed rates assuming the mathematical relationships stay the same between 1 and 8. That may not be necessary as I have found when working in 416 Stainless rifle barrels, slower is better, so I cut tenons and shoulders on E-8 and 135 RPM—which is max speed in the lowest gear range. (I have Dr Marks control setup.) I chamber at 60 RPM and go slow.

The proximity stop doesn’t work too well for me when trying to get a smooth shoulder. I might be doing something wrong, but I get better results by disengaging the power feed with the lathe still turning. The next time I thread I will try the proximity stop, as it should work great for that.

A word of caution. I would not put any weight on anything I have posted. I am still a total newb to machining, though I did get the chamber of my firefroming barrel and the chamber of my match barrel (long range benchrest) virtually identical.
 
Won't get a smooth shoulder because you are cutting sequential diameter passes and the cutter tip is at an angle (not 90 degrees to the face, there is always a relief backwards) so you will get ridges with each pass. Also you are cutting to a stop postion while the cutter is advancing as opposed to dissengaging the feed and allowing the spindle to continue rotating. I always take passes just short of the final face dimension then use the cross slide to face to the final face dimension. Alternative is to face with a cutoff blade and then take passes just shy of the cutoff face. It is a bit of a learning curve, I have changed a lot of my techniques when using the P sensor.
 
I actually thought of doing that way and might try it. I am much interested in threading with the Prox stop. Your video shows the process well as I REALLY like the idea of not having to frantically disengage the half nut and pull back the compound each pass.
 
287934
 
You rock! Saved me from having to do it....
 
Hi,

I know this is a very old post, but do you mind sharing how you calculated this table? Mark mentions above that the TPI will directly correspond to the feed rate which makes sense. However, it is not the reciprocal of the TPI. There is some other ratio involved (approximately 3). I tried to verify your table but I am not able to. Maybe Mark can chime in and explain how this is calculated.

Salah
 
Cross feed is 1/2 the carriage feed rate per top of the feed diagram 1/2 cross feed to 1/1 feed. So 0.004" feed would be 0.002" cross feed. This is pretty typical for most the lathes I have seen, it is also indicated in the front of the 1340GT manual (see below). Most of you cutting feed rates will be in the E1-8 and maybe D6-8 (~0.008-0.003) for this size lathe, the rest of the gearing is primarily for threading. The ratios probably have more to do with threading increments. On this lathe the deepest I typically went in a DOC was around 0.1" (diameter of up to 0.2" in softer materials), steel was typically 0.1" for removal). It all depends on the material and the tooling you are using. (looks like the picture links are broken)
I am trying to figure out what the calculation is. It is not the reciprocal of the TPI. I seem to be missing a ratio of some sort to get from the TPI to the feed rate. Can you help?

Salah
 
Hi,

I know this is a very old post, but do you mind sharing how you calculated this table? Mark mentions above that the TPI will directly correspond to the feed rate which makes sense. However, it is not the reciprocal of the TPI. There is some other ratio involved (approximately 3). I tried to verify your table but I am not able to. Maybe Mark can chime in and explain how this is calculated.

Salah

I know this is an old post but I've wondered this myself.

Can someone explain to an idiot like me how the feed rate is calculated?

I have always just divided the TPI into 1 to find the decimal equivalent but the chart above shows completely different results.

For example I was machining last a part last night using D-6 on the Norton gearbox. The chart on my PM1340GT indicates that D-6 is the gear position for 48 TPI (Threads Per Inch). If you calculate that out isn't is 1/48= .020833 or roughly .021"? Yet in the chart above for D-6 it shows .0068".

Can someone please explain?

Thank you.
 
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