Reducing feed on a PM-1236 lathe

woodrowm

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Good evening - I have a PM-1236 and I need to reduce the feed rate in the X-axis down to .001, the lowest setting now is .002. Is there a way to do this and if there is then how.

Thanks,
Sonny
 
On the printed chart, there is only 3 digits precision so, the non-metric table is rounded-up to 3 decimals. By looking at the metric chart, you can see that position D5 is 0.062 mm/rev and B5 is 0.049 mm/rev. B5 is the slowest x-feed you can set on the machine which translates to 0.00193"/rev. I know of no way to make it go slower other than to use a custom gear on the quadrant rack.

FWIW: Be careful using carbide at that fine of a federate unless you're using coolant of some type.

Ray
 
Hey thanks for the info (not what i wanted to hear) but what is a quandrant rack?
 
Hey thanks for the info (not what i wanted to hear) but what is a quandrant rack?

That's the adjustable arm that the change gears spin on.

BTW: Why in the world do you need such a fine cut? I grow impatient with anything slower than 0.005 IPR and with a properly shaped bit, will give a mirror surface with no cupping artifacts. Also, the finer the feed-rate, the smoother your machine and chucks must be balanced. The slightest bit of an imbalanced chuck or harmonic vibration will look like the footprint of a sasquatch.


Ray
 
The reason why you ask - I want to use a gundrill to drill a .667 hole 30''s deep into some 4140 and the people at Sterling Gun Drills said that I needed to get my feed down to at least .001 for this to work. There must be a way to do this with gear changes ( I would think) any ideas on what the ratio would be.

Thanks,
Sonny
 
The reason why you ask - I want to use a gundrill to drill a .667 hole 30''s deep into some 4140 and the people at Sterling Gun Drills said that I needed to get my feed down to at least .001 for this to work. There must be a way to do this with gear changes ( I would think) any ideas on what the ratio would be.

Thanks,
Sonny


Oh brother, 30" drilling... you picked a fun project all right. Anyhow, the slowest speed on the chart calls for a 24 on top and a 48 at the bottom. Just by looking at the gears, you can see that if a larger gear was placed at the bottom it would make the lower gearbox turn slower. There is a 52 tooth gear in the gear set so, I'd just try putting the 52 in place of the 48 and then measure how much the carriage moves by manually spinning the chuck. That will certainly decrease the IPR and by simple measurement of the difference in diameters of the 48 vs 52, it should be about 10% slower. It also looks that you can put a 22 tooth instead of the 24 tooth and slow it down even more. Give it a shot and let us know. What RPMs will you need to be running at? That little 22 tooth gear will get a workout.

Ray
 
I would try a setup that has a compound gear ratio that would slow the gear box down. Something closer to 2:1 unlike the 120:127 compound you likely have right now. It is the 120/127 transfering from the spindle gear down to the gear box input gear. Using some of your change gears you could replace one of those large gears with a small one and place the gear that you just removed on to the gearbox shaft, or using 4 of the change gears completely replace that 120/127 with 2 compound gearsets.In any case likely you will have to make a special hub(s) to allow this to happen. This is how the change gear lathes are run.
I hope that makes sense.
Pierre
 
Thanks for your input, it looks as though I will be shifting gears tomorrow, by the way the suggested rpm is 700.

Thanks,
Sonny
 
I measured the speed on my leadscrew a while back & posted the values here. D1 is the slowest feed rate on my lathe with the gears set to imperial but I have no idea what the feed rate is. I've been meaning to measure & get a rough estimate. But my PM1236 is a bit different than most, I don't even have D5 & B5 on my chart.
 
The gun drill will need high pressure coolant feed. I think it's around 1200 PSI.
Have you got a pump for that?
Another forum had a suggestion of using a power steering pump.
They should produce the pressure and volume needed.
 
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