ISO General Rule of Thumb(s) - spindle speeds

JID62

JID62

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Good morning all,

In a previous thread I got great help finding specs for a replacement Rocker Shaft for my 101.21400. I was able to make the shaft of out 303 stainless and used a bench grinder to form and shape the cam surfaces. I have a 3/4 HP motor that runs at 3250.

I am going to begin assembly of the drive train this week and have run the pulley/speed calculations for the pulley set I have on hand. The result is an RPM spread of (approx) 3030 down to 740.

I have purchased a "starter set" of tooling from LittleMachineShop with OXA post, holders, index tools, boring set and a tailstock chuck.

I expect to turn mostly nylon, aluminum, soft steel and maybe some 303 stainless or brass.

If anyone can point me to a document or offer thoughts on typical speeds for a lathe of this type, size and the materials noted, I would greatly appreciate. I am certain to do a lot of experimenting and learn as I go, but any hints are always much appreciated.

Cheers,

JID
 
Spindle speed (lathe or mill) for material machining is expressed in SFM (surface feet per minute) - or the rate at which the material passes by the cutter.
Obviously, it couldn't be rated simply in RPM because a very small turning (or mill cutter) would see far less material than a very large turning.
So there's a little bit of 4th Grade math involved to convert SFM to RPM.
There are calculators all over the net. There are Feed Tables all over the net. Easy peasy.
However, there's a catch (isn't there always?). The tables are all based on ideal conditions. If your machine is not sufficiently rigid. If your cutter is not sufficiently robust. If your setup is not sufficiently stable. All of these things contribute to reduced speeds and feeds.
I'd tellya to go get a little green "Machinery's Handbook" which is the Gospel in these things, but they're expensive and many excerpts and resources are already posted. I have one and it was expensive when i got it (replaced) decades ago.
It's a safe bet you won't be able to run "optimum" speeds and feeds on 303 stainless, but nylon and aluminum will be fun and easy.
Welcome aboard.
 
Basic rule of thumb/speed. Us High Speed steel tooling, if your chips are turning any color, yellow, blue, black, your RPM is too fast. Do not try to learn lathe work with Carbide Tooling. Its just not a good idea. You must develop a feel for your work and Carbide Tooling won't let that happen.

The color change won't happen with aluminum, but then again you can't go fast enough to over-heat your tooling while cutting aluminum.
 
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You can download a copy of Machinery's Handbook on line, but a printed copy is much easier to use. These can sometimes be found at used book stores for a reasonable price.
 
First, the best single reference for speeds, feeds, thread cutting and etc. with an Atlas lathe is one of the 30+ editions of Manual Of Lathe Operation and Machinist's Tables (MOLO for short) [published By Atlas between 1937 and 1988. For an Atlas 618 or Craftsman 101.21400 the best editions are probably any of those published after 1957. Atlas shipped one with ever lathe that they or Sears sold after sometime in 1937. The ones shipped with the various Atlas lathes all had an Atlas front cover. Up through 1953, so did ones shipped with the Craftsman machines. Beginning with the 1954 edition, the ones shipped with Craftsman machines had a Craftsman front cover. Up through 1953, all covers were black. From 1954 through 1981, the Craftsman covers remained black while the Atlas ones became light gray. The best place to find one is probably on eBay. Average price is around $30.00, although as might be assumed, the average seller knows about as little about these as most of them do (don't) about most other things sold there.

However, to back up a bit, the motor that you say that you have is not suitable for use on any 6" made by Atlas (or probably on any 6" made by anyone). It is about twice as large and is twice as fast as what Atlas recommended for the machines.. The spindle speeds given on the various speed charts for the 6", 9". 10" and both types of 12" lathes are all calculated based on a motor with a rated RPM of 1725 to 1750. Plus only the two countershafts made for the 10" might be OK with an input RPM that fast. And the largest motor that Atlas ever recommended for the 6" was 1/3 HP. Using a larger motor won't improve the performance of the lathe any. And if you should ever have a crash (I recently gave the only valid excuses for a crash) will only increase the damage done.
 
I was able to download (free) the 1968 printing of the Craftsman MOLO. Also downloaded the South Bend guide, which will come in extra handy when I start work on my SB 9".

I have a alternative motor = 1/4 HP at 1725, cont. duty so I will spin that one up and see what happens... maybe check the brushes first.

I also have another 1/4 HP 1720 that I know works and I can scavenge from a bench sander.

Thank you all for the helpful feedback,

JID
 
Why would there be brushes in a 1725 rpm motor? Universal motor or DC motor sure, but a single phase induction motor?
 
Asm109 said:
Why would there be brushes in a 1725 rpm motor? Universal motor or DC motor sure, but a single phase induction motor?
Click to expand...
My mistake... no brushes, just makes a racket. Sleeve bearing on shaft end is totally shot... junk.
 
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