Trying to part a 2.8" flywheel off bar stock and failing...

[mpanetta]

I am trying my first 'engine' a finger engine (the 2005 NAMES one) and I am having issues I have never had before...

I keep dulling the cutoff tool I am using, I barely get 2 or 3 tenths of an inch done and the tool gets galled (or worse the part grabs it and stops the lathe) and I need to sharpen it again. I have used the same tool on steel, aluminum, and brass of smaller diameter (1.5" or less, including a 1/4" 303 stainless piece) with no issues at all. The piece of stock is an unknown piece of aluminum bar stock of 2.88" in diameter that I have turned down to 2.8".

The cutoff/parting blade I am using is a 1/16x1/2x4*1/2 HSS T shaped blade like little machineshop sells. The stock, lathe, and all the tools were 'inherited' (a friend of the family recently passed) and I have been teaching myself how to use the stuff by making small bits with scrap stock. I have never had an issue with the cutoff tool like this before now.

The only thing I can think of is the bar stock I am using is not 6061 but something harder like 7075... I am feeding a little bit at a time and backing off to clear the chips. I am also starting off with just a short piece of the tool sticking out of the holder and I have increased the length as I cut, all to no avail.

So can anyone tell me what I am doing wrong? Am I just using the wrong tool for the job? Should I just cut the piece off on a band saw or use a hack saw?

Any help would be greatly appreciated! I am hoping to be able to give the engine away for an Xmas present. I think it would be a pretty good one if I can get it done.

Thanks,
Mike

 

[Troutsqueezer]

If you have a band saw with a metal blade, why not try it? If you don't, do you have a Sawzall or similar? You can buy metal blades for those and they cut through thick rod in pretty short order.

 

[Metal Butcher]

Mike, your cut off blade is getting 'galled' with aluminum welding to it. It gives the appearance of a dull tool. This can also happen with an end mill.The cutter gets packed up with chips causing a huge amount of friction and heat at the cutting edge. A slower speed or feed, and the use of an aluminum cutting fluid along with clearing the chips will usually eliminate the problem. I must say that I would never attempt, or recommend using a parting tool to cut-off on such a large diameter, its just asking for trouble. I have a 9 x 20 lathe with a 3/4" spindel bore, and 1 inch maximum diameter on aluminum or brass is the largest diameter I'll attempt, and only if I have no other choice.

Your best bet as mentioned by the previous posters is cutting your work piece blank in a band saw. With its multiple teeth cutting at the same time its much quicker, easier, and safer. It's scary and dangerous when a cut off blade digs in and shatters throwing the pieces back at you. To eliminate the danger I usually rough cut close to dimension in my 4" x6" band saw, and finish up with the machining in the lathe or mill.

Just curios, how big is your lathe?

-MB

 

[doc1955]

If the tool is galling then it is getting to warm use a good supply of oil and use a steady feed what suface speed are you turning at? Are parting off in a 3 jaw chuck? if so keep part of area as close to the chuck a comfort allows you. I like to keep it within .05 of chuck when parting off in a three jaw chuck. Are you sure tool cutting edge is at center line or just ever so sightly below a tool to high will have more friction to over come and will heat up. And if all else fails just cut it off in the band saw and face to correct length.
Good Luck.

 

[mpanetta]

Thanks for all the replies! It looks like using a band saw is the best way to go for something this big. I am using a 3 jaw chuck, normally I would cut off close to the chuck as well but this piece is too big to fit all the way in to the bore (the bore is 2" I think).

The machine I am doing this on is a south bend heavy 10, to answer your question Metal Butcher. I also have a 9x20 but I have not started using it yet. Actually the 9x20 will end up being my machine, the south bend is my fathers.

 

[shred]

A heavy 10 can part off something that big, but it will take a lot of doing and you're going to have a lot of overhang on the parting tool, so it'll want to flex and wander, which will cause jams and breakage, especially with a 1/16" parting tool. You can try getting it perfectly on center, sharp and use plenty of cutting fluid, or you can just saw it and clean up the saw cut. You're very likely to need to clean up the parting cut anyway, so my vote goes for the latter..

 

[RichD]

Along with the other good replies, I've parted 2.375" aluminum off in my 9x20 lathe but I was using my slightly bored out steady rest and supported the tool from below with an adjustable "crutch". It is scary when you dig in. I set the tool at center height.

The crutch and steady rest really work well together. I recently added a threaded hole to the underside of my homemade parting tool holder to simplify the crutch usage (a 1/4x20 cap screw). I lay a smooth 1/2" lathe tool on the top surface of the cross slide and let the head of the cap screw slide on the tool bit as the parting tool gets advanced.
Rich

 

[mpanetta]

So after I exhaust the current stock I have (depending on how many I make or if I want to make something else with an Al flywheel...) would it be worth the extra $$ to buy multiple pieces of stock precut to 1" long vs. buying an x" long piece of stock and cutting it myself? This would include cutting fees of course...

 

[bob ward]

mpanetta, you will have much greater flexibilty if you buy long stock and saw it as necessary. For $200 or $300 you can buy yourself a metal cutting horizontal bandsaw which will serve you well for many years.

There is no way I would attempt to do a part of 2.8" with a 1/16" HSS cut off blade, there is no warning and no second chances when things go wrong. I would definitely be sawing and facing.

 

[Andrew_D]

Definitely saw and face off when possible. It's easier.

However, there are times when you need to part off. I use the same type of blade you refer to (1/16" wide x 1/2" tall from LMS). I use LOTS of cutting fluid. Maybe oil, WD40, <insert favorite blend here> - depends what is being parted.

I've successfully parted up to 2" mystery steel with my 7x12 mini-lathe (repowered with a 2HP treadmill motor). I find that the blade almost seems to be rubbing or whatever and then all of a sudden we're cutting. Keep the feed steady (use power feed if you've got it) & lots of fluid.

Andrew

 

[doc1955]

If you must part off a part a distance from the chuck if you can put a live center in the end of part to help steady part and part off until you are within .2 stop and back off center and finish. The center will help stop the digging in of the part off tool. I've used this process with great success. You still have to very wary of keeping tool lubricated and cool. Any of the soft materials be it steel aluminum bras or what ever some times is a bugger to part off but heat treated and harder materials part off much better.

 

[kvom]

Another idea is to use the parting tool part of the way through, and then cut the rest of the way with a hacksaw.