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I just picked up a well used Bolton Tools BT1022 (10x22) lathe. The previous owner "burned out" the 1 HP motor, so he proceeded to retrofit a 2 HP motor. In order to fit the larger motor, he removed the step pulleys. It is now a 1 speed lathe. I'm going to replace the motor with a variable speed setup. I want to be able to run the lathe slow, and I need to figure the needed pulley ratios. So, what is the fastest speed you feel you really need on your lathe?
Thanks,
John
Depends on the diameter of your work. What you're actually concerned with is surface feet per minute.
The formula I learned in the Navy is SFPM x 12 = PI x DIAMETER x RPM
IIRC the cutting speed for mild steel with high speed tooling is 100 SFPM.
Different materials require different different speeds.
I have a well used Logan that maxes out at 2000 rpm. The fastest I ever run it is about 1200 rpm for polishing, and that's after I disengage the lead screw.
I think it depends on the kinds of things you turn and how you work.Quote:
Originally Posted by John McClanahan
For me: I have several variable-speed lathes (Jet1642 and PM3520b). The min and max speeds possible on these depends on whether the belt is on the higher speed or the lower speed pulleys.
I mostly turn relatively small things and spindles. I usually keep the belt in the high-speed position and I often turn thin spindles wide open, over 3000 rpm. I don't remember the lowest speed possible (not home now) but I think it is a bit over 100 rpm in that belt position on the pulleys.
I often use the lowest speed possible when sanding or letting sprayed or brushed on finishes dry.
Of course, I turn things with larger diameters (bowls, platters, etc.) at a lower speed and large bowls and unbalanced blanks at an even lower speed. I almost always sand at a low speed (or with the lathe off). However, I rarely look at the speed numbers. I just use the speed that "feels right" and sounds right. Usually the faster the speed the cleaner the cut, as long as you have good tool control. I don't know how to learn the best speed except by experience.
JKJ
I am assuming we are talking about metal lathes here in the Metalworking Forum? After owning and operating a metal lathe for nearly 20 years, most of my work has been done at 300-600 rpm. Small things can be ran faster and you can use indexable carbide tooling at higher speeds. Granted this has been hobby not production use. Learn to grind and use HSS tool bits you it will be cheaper and I think you get a better finish.
But I would never go to the problem that your going to have figuring out pulley sizes and belt size needed. Unless you have all the old pulleys and are willing to go back to the OEM motor.
What I have done on two machines, go to a 3 phase motor and put on a VFD. Head over to the Home Shop Machinist forum and do some searching lots of those guys have done exactly what I have recommended. Link> bbs.homeshopmachinist.net/forums/3-General
Sorry, I thought I was on the woodturning.Quote:
Originally Posted by Bill George
I do run my metal working lathes much slower, of course.
JKJ
Mine tops out at 2500. No way I'll run it that fast with a chuck on it, no matter what the chuck is rated for. Collet chuck, sure.
Depends on the chuck size of course, but 1000-1500 can be kind of scary until you get used to it.
I think a better question is "how slow do you need to go"? My metal lathe will go up to 2500 rpm but I have never used it at that speed. It's slowest speed was 60 rpm until I installed a VFD, I use that speed fairly often and have used that ratio and the VFD to go slower a few times. Even with a VFD, you still need some step pulleys or gear ratios.
Thanks for the reply and advise. I understand SFPM. The entire belt and pulley system was stripped off and replaced with a single sheave spindle pulley, so I am trying to figure out if I can make it work. Going fast isn't the problem. Going slow with a single belt is a challenge.
Don't laugh, I've done a bunch of recearch on treadmill motors. There are plenty of You Tube videos of shop tools converted to variable speed with them. I have a treadmill motor and speed control. so I rigged it up for some testing. It does surprisingly well with a 2" pulley on the motor. Good enough that I bored a 1.5" pulley to fit the motor shaft to further improve the low speed torque. I also plan to replace the speed control with one made by KB Electronics.
Besides the motor upgrade, the lathe needs a through cleaning, lubing and adjusting. It will be a spare time project, so it will be awhile before it's completed. I will post an update later.
John
An easier formula to calculate what the RPM should be is RPM= CS x4 divided by the diameter, (times 4 if using carbide). ON a lathe the diameter is the piece being turned. On a mill or drill press it is the diameter of the cutter or drill bit. The cutting speed of mild steel is indeed 100 and a general rule thumb for tool steel is 50. All of this is fine if you are using coolant. IF not I would cut it in half. One can always speed up with no problems but usually the cutting edge gets destroyed or dulls quickly if the speed is to high. Id you are the one buying the drill bits or sharpening the lathe tools I would defiantly use 50 for a cutting speed for mild steel. In industry it is far different .
If you do a lot of drilling small holes with the tailstock then higher rpm can help. For example drilling a 1/16" hole at 1200 rpm would be better drilled at 2400 rpm.
Also center driling with small center drills. The tip of the center drill will cut better at a higher rpm.
Most generally the average sized engine lathe, between 12" to 14" for home use, 2000 rpm would be sufficient for most work, for a higher rpm. Aluminum and brass like the higher rpm range, 1200 to 2000 for aluminum, and for smaller brass turnings, 3000 rpm is not uncommon.
I remember using between 300 and 600 rpm for most jobs on the engine lathe.
I got the lathe upgraded. I found a better speed control that has ramping, dynamic brake, jog and a few other extras. I replaced the pulleys for maximum reduction. It has a speed range from near zero to about 2200 rpms. It could go faster, but I have the max. speed set for 2200. While it does not have the torque of a back geared lathe, I'm not disappointed. This is a major improvement over my mini lathe.
John
I guess anywhere you would combine mineral oil and mineral spirits in a finishing/refinishing application it could be used. I imagine it would clean an old finish and make it shiny. Would I use it as a finish? No way. The smell alone would present a problem.
Do you ever wish you could just suck up all the knowledge floating around in these forums. Especially when it comes to machinist work. Time is cruel indeed. Had to repair a South Bent 10K ( new version) quite a frustrating event. Considered going to a 3 phase and VFD, but in the end I just replaced the motor, pullys, etc. . Just goes from 50 RPM to 1200, but I rarely use anything over 500 to 700 rpm. Mostly work with brass. Thanks for posting. The more I read, the more I learn. The more I learn the more I need to read. And the wheels go round and round. :)