Cutting speeds

Pete Wass · Jun 25, 2013

I have a 10L with two shift levers and a sliding gear. The plaque showing threads and cutting speeds in thousands. How does one figure out where to place the levers to get, say, 90 FPM or 200 FPM?

Thanks,

Pete

johnoder · Jun 25, 2013

Has nothing to do with those levers since you are talking of rotational speeds when you talk of FPM.

One FPM means the work is rotating at a rotational rate of one foot per minute past the tip of the cutting tool. This is diameter dependent of course.

The RPM of a 10" diameter to make 90 FPM is very different from the RPM required to make the same FPM on a 1/2" diameter

Rick_B · Jun 26, 2013

If I remember correctly - John is absolutely correct. FPM is the cutting speed and is material/hardness dependant. Generally the cutting speed can be determined from a table for a given range of material. From there you can calculate the related spindle rpm using the formula 4 X cutting speed divided by the material diameter. Somewhere there is a feed calculation that can be done once the rpm is known that results in an IPR (inches per revolution) feed rate. Starting points for IPR can also be determined from available tables.

Rick

Pete Wass · Jun 26, 2013

OK, Thanks, Now it makes some kind of sense. So what about feed rates? Say I want to reduce the size of a piece of 1" soft Stainless Steel by 1/4", what is the best feed rate to get a great finish. How do I select that feed rate with the two levers and sliding gear? Is there a chart some place I have missed for this. I am correct in believing the feed rate is obtained from the position of these levers and sliding gear, no? This is only one of a number of Black Holes I have always had, not having been trained to be a Machinist and doing the Manly Thing and trying to blunder through

.

Thanks,

Pete

Rick_B · Jun 26, 2013

Pete - like you I am learning as I go - the rule of thumb that I follow is roughing = slow speed and higher feed rate and finishing = faster speed and slower feed. Somewhere on your gearbox there should be a chart - on the left side there should be an indication of how the levers and sliding gear should be positioned and to the right of that should be thread and feed values. The top section indicates how to set the controls for a given threads per inch value using the half nuts. Under that should be a section for inches per revolution using the clutch. A picture of your gear box would be helpful. keep in mind I'm describing a single tumbler gear box but I think the double tumbler works basically the same way.

So far I've found that the slower the feed the better the finish. Fortunately I'm not in a production environment where I need to optimize the variables for efficiency of output and tool life so I can always lean to the more cautious side.

Rick

Pete Wass · Jun 26, 2013

Rick_B said:
Pete - like you I am learning as I go - the rule of thumb that I follow is roughing = slow speed and higher feed rate and finishing = faster speed and slower feed. Somewhere on your gearbox there should be a chart - on the left side there should be an indication of how the levers and sliding gear should be positioned and to the right of that should be thread and feed values. The top section indicates how to set the controls for a given threads per inch value using the half nuts. Under that should be a section for inches per revolution using the clutch. A picture of your gear box would be helpful. keep in mind I'm describing a single tumbler gear box but I think the double tumbler works basically the same way.

So far I've found that the slower the feed the better the finish. Fortunately I'm not in a production environment where I need to optimize the variables for efficiency of output and tool life so I can always lean to the more cautious side.

Rick

Thanks Rick,

Mine is a single tumbler or lever on the gearbox itself. Above there is a three position lever beside the spindle housing that gives two feed speeds by moving it either right or left and a sliding gear at the end of the gear train that gives faster or slower speeds. The only chart gives what you have said. The feed rate is in thousands per inch I believe. What I am looking for is where to set these levers and that gear to get the proper feed rate for whatever material I am using, be it Aluminum or Delrin.

Thanks,

Pete

johnoder · Jun 26, 2013

The chart is self explanatory if you have it. This is the older one when they would cut as coarse as 2 TPI. Later ones would only cut 4 TPI.

What is important is that even though no feed rates are marked on this chart, the chart tells you the relationship between threads and feeds.

It looks like this one says they are 2 1/4 times threads.

This means in the finest thread setting - lower right, 112 TPI, the feed rate will be 252 turns per inch, or .0039 IPR (which is the reciprocal of 252) (assumes the multiplier is in fact 2 1/4 times threads)

Second photo is the later chart, finest thread now 224 (double 112) and with feed rate in inches per revolution (IPR) marked below TPI value

Rick_B · Jun 26, 2013

In John's example look at the far left column of the gear box plate. to get the 112 TPI you would have the sliding gear out (first column), the top lever to the right (2nd column) and the lower tumbler lever engaged in the hole under 112. My particular gear box plate is a little different in that under the thread data there is another section that gives feed rates using the friction clutch. Same concept in terms of the sliding gear, top lever and tumbler though

Rick

Edit - here's a picture of my gear box where you can see the lower section for feed rates using the friction clutch.

ranch1 · Jun 26, 2013

I started the thread shown below some time ago. Check out the youtube video in first post. The post was somewhat flamed by the professionals, but it might be helpful. It is not for setting the TPI, but a method for checking the surface speed of work. Some of the replies in the thread explain better ways for arriving at the surface speed.

http://www.practicalmachinist.com/v...mining-surface-speed-proper-machining-265788/

Pete Wass · Jun 26, 2013

My gear box is like the one pictured except it does not have the lower section on the plaquard that tells the feeds when using the friction clutch. Wonder if they are being reproduced?

johnoder · Jun 26, 2013

Just to avoid confusion, SB was assuming you knew that the friction clutch was to be used when they talked of feeds (on machines with friction clutches). This was irregardless of whether they were expressed as turns per inch (the old way) or inches per revolution (the newer way)

My 24" 1917 Lodge & Shipley made no bones about it. Its finest feed is 88 turns per inch, period.

This is in the same position as 32 threads per inch.

clr8ter · Jun 28, 2013

Sorry to butt in, but;

This brings up a good question....is there an internet source for this type of info specifically regarding SB (10L) lathes? I know the book "how to run a lathe would probably explain it, but I've already spent too much money on this project. I'm wondering at this point exactly how my lathe works. I have run lathes before, but not any this old. I get the general idea, but the specifics are what I don't grasp. Such as; on the single tumbler gear box show above, how easy (or hard) should it be to change gears? On mine, the pin pulls and lever drops easily, but to move it left & right and to get it back up into your new selection can be tough...

johnoder · Jun 28, 2013

but to move it left & right and to get it back up into your new selection can be tough.

Ever oil it? Can make a world of difference.

clr8ter · Jun 28, 2013

Not yet. This thing just landed in my basement a couple weeks ago. It was/is semi in pieces, and is not under power at this time. I still have to order the SB oils, and I have the rebuild book and parts kit.

MetalCarnage · Jun 28, 2013

clr8ter said:
Sorry to butt in, but;

This brings up a good question....is there an internet source for this type of info specifically regarding SB (10L) lathes? I know the book "how to run a lathe would probably explain it, but I've already spent too much money on this project. I'm wondering at this point exactly how my lathe works. I have run lathes before, but not any this old. I get the general idea, but the specifics are what I don't grasp. Such as; on the single tumbler gear box show above, how easy (or hard) should it be to change gears? On mine, the pin pulls and lever drops easily, but to move it left & right and to get it back up into your new selection can be tough...

Well, here's a link to a .pdf copy of How to Run a Lathe It's about 155M but the file is clean. I'm hosting it on my server.

clr8ter said:
Not yet. This thing just landed in my basement a couple weeks ago. It was/is semi in pieces, and is not under power at this time. I still have to order the SB oils, and I have the rebuild book and parts kit.

Not to dampen your enthusiasm for "SB" but I want to let you know that you don't have to get the "SB oils" you see on e-bay. There are commonly available alternatives.

Just FYI

-Ron

clr8ter · Jun 28, 2013

Not to dampen your enthusiasm for "SB"

Not at all. I'm listening.......will check out your File, too. Thanks.

Ferrous · Jun 29, 2013

"but to move it left & right and to get it back up into your new selection can be tough"

If it is still awkward after oiling try holding the slider so as not to cause it to twist left or right. Some wear can make them cranky if you pull the lever sideways with the knob at the end.

Ferrous · Jun 29, 2013

Some basics Pete will help you have some experience without constantly referring to charts.

-Minimum 2 cuts for any job. 1 rough, 1 finish.
-Don't be fooled by "soft stainless". Some is like cutting bubble gum. Look for "free machining".

-RPM = Cutting speed(CS) X 4 divided by the Dia.
-HSS cutting tool speeds for: Hard steel/iron CS = 50 fpm., Mild steel CS = 100 fpm, Soft metal brass/alum = 200 fpm.
-1" stainless steel using CS=50, X 4=200, divided X 1"=200 RPM

-Set feed @ .008"/Rev. for roughing, .003" for finishing. Adjust depth of cut to suit machine power. .030"-.060"
-Always use the friction clutch when turning or facing.
-Only use the half-nuts for threading.
-Keep the tool cutting, never stop the feed and let it rub on the workpiece.
-Mild steel chips should be straw yellow at the most.

-Be carefull with the blundering manly thing, a thoughtful careful aproach is the safe way, both for you and your machine.
-Never trust a 3 jaw! (personal bias)

clr8ter · Jun 29, 2013

Ferrous, excellent rules of thumb! You should turn that into a poster, LOL. NOw, why do you not trust a 3 jaw chuck?

MetalCarnage; What I meant to say earlier is I would like to hear your oil recommendations. And any other suggestions.

MetalCarnage · Jun 30, 2013

clr8ter said:
Ferrous, excellent rules of thumb! You should turn that into a poster, LOL. NOw, why do you not trust a 3 jaw chuck?

MetalCarnage; What I meant to say earlier is I would like to hear your oil recommendations. And any other suggestions.

When I went looking for the actual lubes listed in "How to Run a Lathe" I found that most were long "discontinued". Doing a bit of research I came up with some modern equivalents but there are many more (likely better) options available.

Currently I am using:

DTE 24 MOBIL HYDRAULIC OIL

DTE 26 MOBIL HYDRAULIC OIL

VELOCITE 10 MOBIL SPINDLE OIL

VACTRA #2 MOBIL WAY OIL

All can be ordered from www.use-enco.com and sell for less than $20 per gallon. I'm sure others can provide their recommendations as well.

Hope this helps,

-Ron

Cutting speeds

Aluminum

Diamond

Stainless

Aluminum

Stainless

Aluminum

Diamond

Attachments

Stainless

Plastic

Aluminum

Diamond

Cast Iron

Diamond

Cast Iron

Stainless

Cast Iron

Aluminum

Aluminum

Cast Iron

Stainless

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