Author Topic: Gear cutters in CNC  (Read 1287 times)

Offline steamer

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Gear cutters in CNC
« on: September 25, 2021, 11:35:51 PM »
Lowest speed on my mill is 300 rpm    With a 2.25" cutter that's about 176 ft/min,   which for HSS in 1144 sp is kinda fast.....then again...I've run slitting saws much quicker and they've survived..    What has been your experience?    Usually I follow the 65 ft/min rule, but my Tormach doesn't go any lower....and before I wipe out an expensive cutter, I was looking for someone's who cut at that speed?    I can take 4 passes....no issues
I can also use mist coolant....so should be OK.........

Dave
« Last Edit: September 25, 2021, 11:39:43 PM by steamer »
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Offline steamer

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Re: Gear cutters in CNC
« Reply #1 on: September 25, 2021, 11:38:45 PM »
The cycle is 4 passes to depth of .0694.   then I index the dividing head manually and hit cycle start

Dave
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Offline steamer

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Re: Gear cutters in CNC
« Reply #2 on: September 25, 2021, 11:46:13 PM »
I'm going to finish the cutter arbor, and make up a blank...and If I don't hear by then.....well I'll be the first!.... :zap: :paranoia:
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Offline Craig DeShong

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Re: Gear cutters in CNC
« Reply #3 on: September 26, 2021, 12:22:44 AM »
Hi Dave.

Wish I had some guidance to give you, maybe someone else will.  I run my HSS gear cutters at the prescribed speed for the material Iím cutting, so I have no advice to give you, though I would think a misting coolant should allow you to press the speed somewhat.
Craig
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Offline maury

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Re: Gear cutters in CNC
« Reply #4 on: September 26, 2021, 01:51:59 AM »
Craig, i use a Barber Coleman #3 gear hobber to cut my gears. The hob is about the same diameter as your cutter, and I don't know for sure3, but I believe the rpm is somewhat above 300.
The diffrence is going to be, the hob is immersed in cutting oil all the time it's cutting. This keeps the hob cool and lubricated, as well as washing away the chips.
The only advice I can offer is, keep it wet.

maury
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Offline steamer

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Re: Gear cutters in CNC
« Reply #5 on: September 26, 2021, 01:59:48 AM »
Thank you gentlemen!    We'll   I'll crank the mist lube and keep the cuts light.  I bought the smallest diameter cutters I could find but I thought I could go lower....but the "butt dyno"  says  go for it.... 8)     Now I need a good 1/2-20 bolt and I'm good to go!.
« Last Edit: September 26, 2021, 03:20:20 AM by steamer »
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Offline john mills

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Re: Gear cutters in CNC
« Reply #6 on: September 26, 2021, 03:10:18 AM »
if that is your slowest speed it will have do with constant spray mist coolant it hopefully will last what was the material the gears are made off.
john
you could always try a similar material as the gears at the dia of the cutter in your lathe  and a ground high speed steel tool and see how it lasts you could use a different dia as long as it is same cutting speed that would give a better idea of how it would last.
« Last Edit: September 26, 2021, 03:30:20 AM by john mills »

Offline Jasonb

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Re: Gear cutters in CNC
« Reply #7 on: September 26, 2021, 07:16:11 AM »
What MOD or DP are your gears, I've generally found it better to do them in one pass unless very large teeth rather than several which just blunts the tips more, at the most take out the majority with one pass and then a light finish pass.

I've not had a speed readout on the manual mill for most of it's life so can't say what I have run at in the past but suspect it's 300+ and like you I find I have to run slitting saws at faster than calculated as the hobby variable speed machines can stall at low revs with large dia cutters.  If I do work out a speed then I tend to work with 30m/min for HSS and 100m/min for carbide on steel which is towards the high side.

Looking at your F360 screen shot is it possible to set the staydown to a higher percentage as there will be a lot of up and down in Z between each pass that is not really needed, you could just back out slightly in Y after a cut and then Z to return to start. If you were doing it on a manual mill then I expect most would not alter the height and maybe not even back the tool out in Y when reversing So maybe even do away with the retract height and just have the tool set on ctr height so you don't waste time with Z movements.
« Last Edit: September 26, 2021, 07:33:15 AM by Jasonb »

Online Vixen

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Re: Gear cutters in CNC
« Reply #8 on: September 26, 2021, 08:31:32 AM »
Hello Dave,

I agree with Jason, small gears (1.0 Mod, 24DP or smaller) are best done in one pass. This reduces cutter wear considerably. The cutters I use, come from China and are HSS. My spindle speed is 100 to 200 RPM-ish. I apply lots of coolant/ lubricant with a brush, it cools the cutter and washes away the chips. I make the cutting pass, retract the cutter a few thou before returning to the start position and indexing the blank. I then go round once more, as a light finishing pass at the same setting. There is no need to move the cutter in Z axis once it has been set true to the gears axis.




You may be interested to hear about the durability of the inexpensive Chinese involute gear cutters which are currently flooding the market. I have now cut over 400 teeth with one individual cutter in EN8 steel, which is not the friendliest of steels to machine. I can now see wear marks on both sides of each of the cutter's teeth. That cutter is no longer as sharp and keen as it once was. I estimate the wear to be about 0.001" (0.025 mm) off both flanks, as I need to advance the depth of cut by an additional 0.005" to maintain the correct tooth contact at the PCD.

So, use plenty of coolant, if it smokes then apply more, lots more.  :smokin2:

Mike

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Offline john mills

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Re: Gear cutters in CNC
« Reply #9 on: September 26, 2021, 09:27:54 AM »
i would prefer to cut teeth in one pass  it will leave the wear marks on the cuter even if you do multiple passes
the cutter will end up with wear lines with will leave marks in the finish on the finished teeth running a light finish cut to take out spring on a light machine is ok.
I sobbed gears on a hobbing machine i had to think about 1 pass but it went no problems and that was 3 1/2DP
american stub form the shopper i used that also cut in one pass 2.5 modul your small teeth should cut ok.
John

Offline jadge

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Re: Gear cutters in CNC
« Reply #10 on: September 26, 2021, 11:31:01 AM »
I learnt early on that taking multiple passes when gear cutting is a waste of time. Now all my manual gear cutting is done in one pass. This is a 5DP gear cut in one pass:



The cutter was running at 60rpm and the material is cast iron. Cutting was done horizontally as the gear was too big to fit under the arbor when vertical.

If making a gear on the CNC mill I don't bother with involute cutters. Simply design the gear in 3D CAD and use standard ballnose cutters. Here's a 10DP steel pinion being cut with a ballnose cutter:



If nothing else it solves the problem of needing low speeds. The pinion with mating internal gear:



At one time roughing cut involute cutters were available. But only for 1/2DP gears and upwards, which are larger than I'm ever likely to make.

Andrew

Offline steamer

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Re: Gear cutters in CNC
« Reply #11 on: September 26, 2021, 12:32:18 PM »
What MOD or DP are your gears, I've generally found it better to do them in one pass unless very large teeth rather than several which just blunts the tips more, at the most take out the majority with one pass and then a light finish pass.

32 DP
 I've cut quite a few gears before...but as I pointed out in my original post, not with THIS machine...I need to adjust to what THIS machine can do.   It may not have torque to go full depth  Actually I'm fairly convinced it wont!       What I may do is "Gash" the teeth with a saw, or an endmill and then finish with the gear cutter to full depth.

Dave
 
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Offline Jasonb

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Re: Gear cutters in CNC
« Reply #12 on: September 26, 2021, 01:01:50 PM »
I've cut a fair few 32DP and MOD1 (25.4DP) on my X3 with single passes so your Tormach should be upto it, I would be happy doing that size on the KX3 CNC in one pass. The MOD1 cutters being the cheap far eastern ones are 50mm dia so can be run a little faster rpm wise but teh 32DP are the same dia as yours.

Offline steamer

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Re: Gear cutters in CNC
« Reply #13 on: September 26, 2021, 01:54:39 PM »
I've cut a fair few 32DP and MOD1 (25.4DP) on my X3 with single passes so your Tormach should be upto it, I would be happy doing that size on the KX3 CNC in one pass. The MOD1 cutters being the cheap far eastern ones are 50mm dia so can be run a little faster rpm wise but teh 32DP are the same dia as yours.

At what speed Jason....
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Offline Jasonb

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Re: Gear cutters in CNC
« Reply #14 on: September 26, 2021, 01:59:39 PM »
As said earlier "I've not had a speed readout on the manual mill for most of it's life so can't say what I have run at in the past but suspect it's 300+ "