Cut off cycle time

[Vern Smith]

I'm talking myself into buying a CNC lathe and considering that I need a good engine lathe as much as I need cnc the TL-1 or 2 look like a good choice. One thing I do rather consistently is saw off pucks in 6061 for use in the mill. I also make a lot of thin pulley flanges. I was hoping the TL would justify itself for these operations.

Assuming the max rpm of 2000 can you fellows give me an idea of the time it will take the TL to part off a disk from a 2.5" diameter bar and a 1.5" diameter bar assuming a .5 hole is already drilled in the center. I would think I would need coolant for these operations as well.

Vern

[HuFlungDung]

In aluminum, you'd almost be running full speed right from the start. So if feedrate is .004/rev, then the cross slide would be moving at 2000*.004= 8"/minute. So about 8 seconds for the 2.5" diameter (1" radial cut) plus spindle acceleration time.

[Geof]

If you ask and say pretty please with sugar on it I might do an experiment for you.

We part off pucks of 2-1/4" and 2" 6061 all day long, and 2-5/8" leaded.

You will certainly need coolant.

I think starting at 2-1/2" diameter at 2000rpm is a bit optimistic, our experience is that often the parting blade can develop a shimmy at high sfm; probably something around 1000 rpm would be a good starting point. Which of course doubles your part-off time. You also need to slow down to something like 500 rpm just before the piece comes off to avoid having it bounce around too much.

I don't want to discourage you from getting a TL machine, I think they are a great buy, but a 10" miter saw with a triple chip carbide blade will bang off your 2-1/2" diameter pucks far quicker than parting them.

[Vern Smith]

That would be a lot better than cutting them off with my el cheapo horizontal band saw which takes about a minute and a half. It would also give me a presentable finish which the band saw does not. Is parallelism of +- .003 reasonable to expect when parting off a 2.5" diameter puck? Would the part off tool width for this job be .125 or could you get away with something thinner?

Geof, your pragmatic suggestions are not helpful when I'm trying to justify an extravagance. I would like to take a rain check on your graciously offered experiment. If I buy the new toy I'm sure I will need lots of help from you fellows and don't want to wear out me welcome early.

Anyone have a seat of OneCNC Lathe they want to sell cheap?

Vern

[Donkey Hotey]

Originally Posted by Vern Smith That would be a lot better than cutting them off with my el cheapo horizontal band saw which takes about a minute and a half. It would also give me a presentable finish which the band saw does not. Is parallelism of +- .003 reasonable to expect when parting off a 2.5" diameter puck? Would the part off tool width for this job be .125 or could you get away with something thinner?

My limited experience says that parting produces an irregular finish when parting that kind of diameter. I've sometimes had a parting tool push one way or the other, more than 0.030"--especially toward the center where SFM falls off. I would not count on a TL cutting finished blanks with nothing more than a parting tool. Count on another finishing step.

Also: you asked about finish. You're not machining those two sides after sawing? Why not?

My advice (at least for your slugging part): buy yourself a better bandsaw. I bought a very nice, coolant fed, 9x16" horizontal for $800 on eBay. With the bad economy, there are plenty of used saws out there and you might even do better than that.

I don't know what kind of quantities you truly need, but I'll bet you could buy a used, auto-feed saw on eBay for less than $5K. That thing would create slugs all day long with little attention.

[Geof]

A 0.125" tool is a bit thin for 2.5" diameter but you do have a hole so maybe it will be okay; a narrow tool is more prone to the shimmy I mentioned.

Parallel to +/-0.003"? Yes, probably but not necessarily smooth. Have a look at the pictures in post #17 in this thread discussing parting aluminum.

parting off aluminum

[Vern Smith]

Geof,

I have noticed over the last year or so that you either have a encyclopedic memory or some system to catalog threads on these forums. Is there a feature somewhere on the forum that provides this capability that I'm too dull to find?

It looks like getting good part off results takes more than a little work with proper set ups and tooling. What else is new.

Vern

[HuFlungDung]

It would probably be a good idea to incorporate a facing cycle to reface the end of the bar between part offs. I think maybe I've seen an attachment somewhere that fits on a cutoff block to hold an insert for this purpose. But you need sufficient overtravel of the X axis to make it happen.

8 seconds is a long time. Should easily be done a part off in that length of time. I run CSS and usually let her run right to the max. I use 1/8 part off blades. The cut doesn't shimmy, but it may not be perfectly flat, it is difficult to predict if the blade will deflect a little, but usually a new insert cuts straight. You must have spindle liner support to keep the bar from vibrating. This could be a cause of shimmy and vibration in cut.

If your bar stock has a hole in it, you could rig up a catcher in the tailstock chuck: a short wood dowel will work, maybe 3/8" in a 1/2" hole. Use a piece of wood so it can break off if something goes wrong.

[Geof]

Originally Posted by Vern Smith Geof, I have noticed over the last year or so that you either have a encyclopedic memory or some system to catalog threads on these forums. Is there a feature somewhere on the forum that provides this capability that I'm too dull to find?... Vern

Encyclopedic is a bit strong but I do have a good memory for some things. The 'some things' does not include names, birthdays, anniversaries, etc which has caused a bit of grief occasionally.

If I have read it I will often remember it even if I cannot exactly identify the source. This was real handy at university writing exams, I could close my eyes and visualize entire pages of lectures notes and copy them sometimes almost word for word. That caused me a lot of grief once when i was accused of having crib sheets. Just a freakish brain I guess.

But I do have a bit of a trick here on CNCzone. If I remember posting a picture I can find it in the Attachments on the User CP page and it gives me a link to the thread.

Hu's idea to face, and do it without indexing the toolchanger is the way to go. If it is not possible to mount something after the parting blade you could mount the parting blade at the back upside down and have the facing tool in the toolpost. On the TL programming a tool to come in from the back is a bit funky because you have to have your signs on X backwards.

[JohnJW]

Originally Posted by Geof I don't want to discourage you from getting a TL machine, I think they are a great buy, but a 10" miter saw with a triple chip carbide blade will bang off your 2-1/2" diameter pucks far quicker than parting them.

Geof,

What type of miter saw and blades do you recommend? I think if it'll work for 2.5" D round bar it should probably also work for 1" square bars. I want to cut some 1" aluminum squares cube from a bar stock and originally I thought about mounting 30" section of the bar and milling out the 1" cubes but I think I will waste a lot of material that way. Horizontal bandsaws seems like it's more difficult to operate for small pieces and more expensive for low volume cutting.

thanks,

John

[Geof]

Originally Posted by JohnJW Geof, What type of miter saw and blades do you recommend? I think if it'll work for 2.5" D round bar it should probably also work for 1" square bars.... thanks, John

Excellent for something that small.

Almost any good quality miter saw will do but I looked for the lowest blade speed available; I think it is a De Walt.

Get the 'Triple Chip' carbide blade with as many teeth as you can find. These are the blades with alternating square cornered teeth and teeth that have bevelled corners; they will be labelled suitable for nonferrous metal or aluminum. The best blades are the type that have laser cut squiggly gooves in the blade which are filled with a rubbery compound. These are to prevent blade warping if it gets warm and the rubber dampens vibration so they cut very quietly. I think the make if Freud but I am not at the business to go have a look.

Also get a mister to spray a very small amount of coolant on the blade, it helps with the surface finish.

We also made a fixture to hold the material which is a block with a hole that the stock slides thru with the blade coming down through a slot. This way it cannot get lifted and jammed in the blade and the cut off piece is retained in the hole until you advance the stock and push it out.

[Vern Smith]

At the risk if going a little off topic I want to be sure I understand the capabilities of the TL machines. Haas offers a pneumatic collet closer with a foot pedal for the TL machines made by Royal. Royal also offers a bar puller as well as a bar puller/cut off combined. The collet closer feeds through the spindle bore and is hollow. If I cut bar stock to lengths no longer than the length of the collet closer tube ( and install properly sized spindle liners) can I use the bar puller to automatically advance the bar?

I know this is doable with pheumatic chucks and maybe I would be better off with one of these when utilizing a puller? I liked the looks of the collet chuck in case I crash during the learning process it would not be into spinning jaws.