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Speeds and Feeds Question

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ptrotter

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#1
I am ready to start trying my new PM1340GT and my first project is a couple of small chuck keys for my Bison 8" 4-jaw combination chuck. I have a piece of 3/4" O2 tool steel I hope to use and am trying to figure out the proper speed and feed to use. I will be trying the coated CCMT3 carbide inserts I got with the tooling set I bought with the lathe.

When I look up O2 steel in the Machinery's Handbook it tells me to use a speed 830 SFM and .017 in/rev feed. This corresponds to 4229 RPM which is way above anything I can get on the machine. What would be a realistic RPM to use? Also, if I read the feed table on the lathe correctly, I should put the left gear lever in the "C" position to get a feed of approximately .017 in/rev. Am I reading this correctly? And what about depth of cut?

As you see, I have a lot to learn.

Thanks for any advice.
 

T Bredehoft

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#2
Since you can't achieve terminal speed, set it where you feel comfortable. Possibly nearer 500 to get started with. At 4200, .017 feed, you couldn't shut it off fast enough. I'd think .005 feed and .100 depth would be good to start with. You'll have to learn what you are comfortable with. Maybe 500 would be too fast to begin with, try 125 or so. You're going to have hot chips flying all over (maybe) and you won't be expecting them. Starting out is a crap-shoot, you don't know what to expect, so go on the 'take-it-easy' side until you know what to expect. You won't hurt anything going to slowly.
 

mksj

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#3
Speeds and feeds for inserts are centered more around production machines and high Hp, as opposed to smaller lathes. I usually run my lathe speeds/feeds at about 1/4-1/2 of what is printed on the insert boxes. Feeds are predominately around 0.004"/rev, with a range of 0.007-0.002"/rev. The DOC is often determined by the insert nose diameter and also if the insert is molded (CCMT) vs ground (CCGT), the latter being much sharper and able to take finer cuts without the nose of the insert deflecting from the work. I typically use a 32.51 insert size, so typically the minimum DOC is around 0.002, the maximum cut on the 1340GT is in the range of 0.1-0.15 diameter with a feed in the 0.004-5" range. I rarely use a 32.52 insert, dut it requires a slightly deeper cut probably on the order of 0.004-0.006", and give a very nice finish. A CGGT type can take a smaller depth cut, but I would get these inserts on different materials to get a feel of DOC and feed for your machine. Aluminum you can push faster speeds. The brand/quality of the insert can make a significant difference in how well they work. My go to insert for all steel (they will also work ok in aluminum) is an Iscar ISCAR CCMT 32.51 or 3-2-SM IC907 CCMT09T308-SM
https://www.ebay.com/itm/10-pcs-ISCAR-CCMT-3-2-SM-IC907-CCMT09T308-SM/323271443088

On 3/4" stock I am running the RPM in the 600-800 RPM range for O1 steel, aluminum you can turn faster but I get a clean cut also at this RPM. On steel you can look at the chips to see the color (straw color, then turning blue after they come off) to see if you are pushing too hard. Higher feed rates will help break the chips into C's as opposed to long strings, but sometimes the machine does not have the ultimate power and rigidity to remove high volumes of materials. Every material turns differently and will show a remarkable difference in finish based on speed and feed, I found with steel I needed to increase my feed rate to around 0.004-0.005"/rev gave a much better finish then slower feeds. When targeting a final dimension, as I get closer to the target dimension I will take something like one or two 0.01" passes and look at my DRO reading and measure the actual cut diameters to compare the two. Then adjust the last pass to compensate for the difference. Typically I can hit 0.0005" dimensional accuracy.

If you are pushing too hard on turning or drilling you will get some chatter or singing, so that is the nice feature of the VFD that you can adjust the speed on the fly. I find this is a significant factor when drilling and boring, so my MT3 drills, something like a 3/4" will be happiest at around 250 RPM, a 1/2 drill around 400-500 RPM, 1/4" around 800 RPM into steel with some lube and periodically clearing the chips.

Below are some chuck keys for the Bison I made a long time ago, I cut the square using a collet block on the mill and used a file to tweak the final fit. I relieved the back end to decrease the weight and added a small set screw that holds the T handle in place. I use a small magnetic in the tip of each key so they don not fall out when rotating the chuck. I set up a 0.0001" reading dial indicator in a QCTP holder which makes for very quick work of dialing down the TIR. I like the Starrett 25-511 or 25-611 series dial indicators because of the range (0.2") and resolution (0.0001"), sometimes they come up in good used condition for around $80 or new for a bit more. There are some inexpensive imports as an alternative, but I use one dial indicator and one test indicator for pretty much everything, it was worth buying once. When checking the TIR on the lathe I often use the JOG function for final reading, turning by hand can introduce more variation when turning the chuck.
https://www.ebay.com/itm/Brown-Shar...001-0-5-0-Rotating-Dial-Lug-Back/162914577775
https://www.ebay.com/itm/Starrett-25-611J-Dial-Indicator/292554013714

20161218_125109.jpg Bison Chuck Keys.jpg
 

ptrotter

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#5
Tom and Mark,

Thanks for your response. I appreciate all of your help. So far so good. I started on my chuck keys. Got the bodies done. I think they turned pretty good for the first time using a lathe other than my Sherline. Now to drill the hole for the handle and square the ends. Without a mill that will be a little more difficult but I'll figure out something.

Key.jpg
 

shooter123456

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#7
Tom and Mark,

Thanks for your response. I appreciate all of your help. So far so good. I started on my chuck keys. Got the bodies done. I think they turned pretty good for the first time using a lathe other than my Sherline. Now to drill the hole for the handle and square the ends. Without a mill that will be a little more difficult but I'll figure out something.

View attachment 269092
Looks good! To drill them without a mill, you can stick them in the lathes 4 jaw and drill, or stick a drill bit in the 3 jaw, put the key bodies on the lathes tool holder and drill like that.
 

ptrotter

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#8
shooter123456,

Never thought of that. Thanks. I do have a good drill press so drilling is really an issue, but I might try your idea to see how it works.
 

ptrotter

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#9
Well I finished my small chuck keys. I think they came out pretty good for my first time using this lathe. I ended up cutting the square ends on my Sherline mill. It took some time but ended up pretty good. My knurling needs a bit of work so I will need to practice a bit. I put small magnets in the tip like mksj did and I need to face the front a little to make the magnets come out flush with the face. Over all I'm quite pleased. Next project is a spider. Each project seems to need new skills. On the spider I will get to try boring.

Chuck Keys.jpg
 
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