[mntn-biker]

I am researching benchtop mills in preparation for a bike component product line I want to start mfg. I am very interested in the Tormach PCNC 1100 but was wondering if anyone has some information on milling stainless. I need to make some intermittent ~.030" deep cuts on some gear teeth with a 3/4" diameter ballnose carbide cutter. I am basically putting a bevel on these teeth with this cutter. My question is will this mill handle this size cutter and a ~.030" depth cut? I would think it would since it is a very shallow cut but you are all the experts on these machines. Also, I will be doing some engraving with some 1/8" shank, 1/16" diameter tip carbide ballnose cutters with a depth of ~ .003" to ~ .005" deep. Curious if I should be considering the speed attachment to get the ~15k spindle speed? These mills seem quite stout and built quite well from everything I have seen or heard so far. I am looking at the 1100 due to a part requirement of taking advantage of the larger Y axis travel.

Thanks in advance for your input!

Mike

[Don Clement]

Why do you need to use such a large tool with CNC? Why not use a smaller tool and using software have the CNC generate the needed curve?

Don

[mntn-biker]

Why do you need to use such a large tool with CNC? Why not use a smaller tool and using software have the CNC generate the needed curve?

Don

Since it is such a minimal depth cut (putting a "bevel" on the gear teeth), I was figuring on 1 pass. Sure I could use a smaller cutter with multiple passes but if a larger cutter can give me a "bevel" in 1 pass, wouldn't that be quicker? I already have the carbide cutter in hand that was used in my prototyping. Rather than a flat angled bevel, the resulting bevel is actually a 3/8" radius. I just created an image of my part and found I am actually only cutting .019" deep with a 3/4" ballnose cutter. I attached an image in here but it didn't show up so here is the link instead:

https://picasaweb.google.com/lh/phot...eat=directlink

[Don Clement]

Sounds like manual machine thinking. CNC can set you free from manual machining thinking and in fact to best take advantage of CNC one must think differently from manual machining. Thread milling for example. Taking smaller cuts and letting software worry about using multiple passes.

Don

[StephanWenger]

What Don says: all true. Once you got used to CNC, your choice of tools will probably change.

Then again, for such a light cut, I don't se a reason to use a large cutter when the geometry makes it possible, CNC or not.

With respect to the original question, I have used 20mm indexed cutters for slotting in 314 with a depth of 2mm (roughly 3/4" for the diameter, and a bit less than 1/8th" depth). Running at 50mm/m (roughly 2 ipm), 300 rpm in low gear, with flood coolant; absolutely no problem. You can probably go much faster if this is a production run and time is money. For me, hobbyist, time is not money, so I kept the feed rate low.

As for the engraving: for cost efficient production, and to get a decent finish, you will need the speeder or one of the high speed spindles (preferably not the proxxon for stainless). My hunch is that in stainless, 15000 rpm should be fine with a 1/16 cutter, so the speeder would be my choice, considering how simple the setup is. For the shallow cut you need, I would start at 10 ipm, and ramp up to faster speeds if finish and cutter live is to your liking.

Stephan

[mntn-biker]

Please pardon my ignorance but it just seems to me that making 1 pass reduces cycle time tremendously. Cutting the same geometry would take multiple passes (number of passes = stepover?) to cut this .375" radius on the part. Bear in mind that this is an approximately 6" diameter part we are cutting. I am a newbie to hi speed cnc milling but I can be accused of "manual machine thinking" due to my years of building sheet metal stamping dies in the tool and die trade. About the time cnc's were getting introduced into the smaller job shops is about the time I entered the design end of things so I have "0" experience operating a cnc mill. I have ran wire edm machines so I have a limited understanding of g-codes.

[StephanWenger]

Hi,
if you have such a perfect match between the geometry you want and the tools available (and the machine can handle the tool, which, in this case, I think it can), then there is no reason not to use it.
However, if your parts were requiring more complex operations, chances are that you would save time using a more universally useful cutter (compared to the rather exotic than a 3/4" ball end), and have it running multiple passes. the tool change between a "more useful cutter" and the 3/4" requires operator attention, additional setup time, and at the end may cost you more time than the multi-pass. At least one a machine like the Tormach.
I hope your 3/8" radius has no great requirements on precision. If it does, keep in mind that most cutters are a little bit "under" in diameter. Compensating for this, for a slotting operation, that usually results in two passes anyway.
Stephan