# Reducing feed on a PM-1236 lathe



## woodrowm (Apr 15, 2014)

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


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## Ray C (Apr 15, 2014)

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


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## woodrowm (Apr 15, 2014)

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


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## Ray C (Apr 15, 2014)

woodrowm said:


> 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


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## woodrowm (Apr 15, 2014)

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


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## Ray C (Apr 15, 2014)

woodrowm said:


> 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


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## pdentrem (Apr 15, 2014)

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


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## woodrowm (Apr 15, 2014)

Thanks for your input, it looks as though I will be shifting gears tomorrow, by the way the suggested rpm is 700.

Thanks,
Sonny


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## darkzero (Apr 15, 2014)

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.


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## tertiaryjim (Apr 15, 2014)

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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## Ray C (Apr 15, 2014)

tertiaryjim said:


> 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.



FWIW, 1200psi is nothing to play games with and pressures like that at close range will tear flesh in a nasty way.  If you do obtain/use such a pump, caution and care are the theme of the day...


Ray


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## Ray C (Apr 15, 2014)

woodrowm said:


> Thanks for your input, it looks as though I will be shifting gears tomorrow, by the way the suggested rpm is 700.
> 
> Thanks,
> Sonny



At 700 RPM, you won't have any problems spinning a 22 tooth against the large gear.

Ray


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## woodrowm (Apr 16, 2014)

Just to let you know after the gear change (top 22t middle 127t and lower 52t) the best I could get was .018 feed rate, so if I have done my math right if I use top 24t middle 127t and 96t lower I should get somewhere between .001 and .0009 feed rate. Now to find or make a 96t gear.

Does anyone know if the gears in the PM1236 are standard or metric.

Now for the air pressure after talking with Doug (great guy, knows his stuff about gun drills) at Sterling Gun Drills you can run a spray mist system with shop air (they sell a unit just for this but out of my price range) for what I am doing.
So his suggestion was to get a Bijur Spray Mist System off of e-bay (which I did for $185 free shipping) and send it to him and he would make sure that it will be up to what I am doing.

Thanks,
Sonny


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## Ray C (Apr 16, 2014)

woodrowm said:


> Just to let you know after the gear change (top 22t middle 127t and lower 52t) the best I could get was .018 feed rate, so if I have done my math right if I use top 24t middle 127t and 96t lower I should get somewhere between .001 and .0009 feed rate. Now to find or make a 96t gear.
> 
> Does anyone know if the gears in the PM1236 are standard or metric.
> 
> ...



Hmmm, don't know the specs on those gears and will try to get some info for you.  

By any chance, did you try it with a 24/127/52 combination?  Maybe I was seeing things wrong and that a larger gear at the upper position will get you in the desired ballpark...  For sure though, you want a larger gear driving the bottom gearbox.

Ray


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## woodrowm (Apr 16, 2014)

Hey thanks Ray any info on the gears would be great.

Thanks,
Sonny


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## george wilson (Apr 17, 2014)

I found some extra gears for my Grizzly 16" lathe. I can double or halve the threads and feeds indicated on the QC box. That is good,since the QC box does not originally have the number of available threads I'd really like to have. It does now! Also,my lathe would only go 60 RPM as delivered,which is ridiculous for a machine that can swing 24" in the gap,or only for use over the ways. I made a 2 step pulley and halved the speed range. At least the lathe will do 30 RPM now.( I wish it would do 15 RPM.) Modern lathes are chronically made to run TOO FAST.  I'm not too concerned about halving the high end speed. I have a Hardinge HLVH for small work.

I always have collected gears where I can,and it has paid off a few times. My Harrison milling machine has an old fashioned power feed that uses change gears to change the speed. I found out that old 6" Atlas lathe gears work just fine on it. It would be a major pain to remove the old power feed and modify the mill to accept a Servo power feed. Someone was offering to make gears for several hundred dollars for 2!! I'll use the Atlas ones!!(I could have made them anyway). Fortunately,I have a Bridgeport type mill with a Servo brand power feed on it. Also,I have a Deckel fp1,but have yet needed to use it. Just too used to my Bridgey,and have many attachments for it.

The message is,COLLECT gears. There are always gears for sale on ebay. Of course,you have to have the correct teeth.


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## Ray C (Apr 18, 2014)

OK, just spoke to Matt... No, he doesn't have specs on those gears about pitch, pressure angle etc. I'm not sure if they're 14's or 22's...
  I'll be in the shop later today and see if I can measure things.


Ray


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## woodrowm (Apr 19, 2014)

Good morning - That would be great any info would be helpful, by chance do you know if they are metric or standard I ask this because I need to make a 96t gear to get the feed that I need. If they are metric i need to get a #7 involute cuter if it is standard I would need a #1-1/2.

Thanks,
Sonny


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## Ray C (Apr 19, 2014)

Hi... Sorry for the slow reply. 

OK, the circular pitch, as best I can measure, is 0.146" (3.71mm).  Width of all the gears (not that it really matters) is 0.392" (9.96mm).

Ray


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