Fly Cutter RPMs, etc.

[John TV]

So your calculations sound correct but 4" seems like a fairly large fly cutter, do you need it that large, is there a lot of stick out? I would think your machine will tell you a lot after just a few seconds of cutting. I think if it were me I would start at about half that speed and experiment a bit. Also would try to keep stick out and depth of cut reasonable. Again, I'm so new to this I'm not sure that I am adding anything to this thread but it's still fun learning from all these members.


Sent from my iPhone using Tapatalk

 

[devils4ever]

Depending where I look, I see vastly different values for SFPM.

I'm using a HSS cutter with minimum overhang. I'm guessing the diameter to be about 4", it might be a little less.

I'll see if I can get a slide rule calculator. That might help a lot. Plus, I'll try different RPMs and see how it works out. I'm assuming I don't want to go above 1500 or so RPMs? Is it safe to go higher on my PM-25MV mill?

 

[MrWhoopee]

I tend to be a little more conservative than John (at least with HSS), but still in the same range. Using 80 SFM for mild steel, (80x4)/4= 80 rpm. In aluminum, (200x4)/4=200 rpm. In no case will you even get close to 1500 rpm with HSS and a 4 in. flycutter. Unless the cutter is balanced, I suspect that the vibration would become unnerving before you hit 1500 regardless. Cutting speed is not the only limiting factor, it's just the last one when vibration and rigidity permit higher speeds.

Once you start to get the feel for this stuff, you will do these calculations very quickly in you head. Cutting speeds are not hard & fast numbers, they just get you into the right range to prevent destroying the cutting edge on the initial cut. Start low and work your way up. If you're running production on a CNC, you want to minimize cycle time which requires maximizing stock removal. As a hobbyist who is paying for his own tooling and not charging by the hour, other factors are more important.

 

[Driveslayer45]

I have recently been using a fly cutter for various projects. the most recent flattening 1.75" wide stainless, 304 maybe. i am using a soldered carbide cutter about 1.5" diameter. i found i had to take deep cuts or my carbide would get dull quickly. running at ~700 rpm, not sure of the feed rate, but cuts at .015 would dull cutter, cuts .040-.050 worked great with beautiful curled chips. i am running right down the center and my cutter is taking a full width cut.

mill is a pm727v

 

[MrWhoopee]

I have recently been using a fly cutter for various projects. the most recent flattening 1.75" wide stainless, 304 maybe. i am using a soldered carbide cutter about 1.5" diameter. i found i had to take deep cuts or my carbide would get dull quickly. running at ~700 rpm, not sure of the feed rate, but cuts at .015 would dull cutter, cuts .040-.050 worked great with beautiful curled chips. i am running right down the center and my cutter is taking a full width cut.

mill is a pm727v

I would say that 700 rpm is at the very high end of what you can expect from a brazed carbide (USA or China?) in 304, but since it holds up with a heavier depth of cut, that's not the problem. My guess would be that at .015 DOC the cutter is doing more rubbing than cutting and the material is work hardening.

 

[ltlvt]

Yes, the speeds should be the same regardless. I have no idea why they even have two different charts. It's all about the the relative speed between metal and cutting tool. That speed for milling aluminum is too high.

None of the links are useable. #404 not found.

 

[higgite]

Could be because they're over 3 years old.

Tom

 

[Flynth]

Could be because they're over 3 years old.

Tom

Indeed the thread is 3 years old, but as it was bumped already let me add a huge fat warning to anyone with PM-25MV or another version of the same Chinese mill that tries to use a fly cutter, especially a hss one.

The same warning applies to popular 3 insert facing cutters and use of boring heads.

Take the smallest cut you can, or better yet, don't use a fly cutter, or any cutter with diameter over 20mm for an interrupted cut on this mill. I've destroyed a two speed gear in my mill by using a fly cutter. Taking a 20 thou cut running at slightly under 100sfpm. It run great. I was facing a 2in wide piece of mild steel. It lasted about 3m (9ft).

Those mills use a plastic(nylon) two speed gear and teeth of those geers shear off very easily on the lower setting. Facing this 3m piece (moved manually, checking depth of cut each time it sheared all the teeth.

Thankfully I bought my mill from a local importer, not straight from China and they sent me that gear free of charge. BTW, getting to that gear was not easy either. You need to remove the motor, remove the (heavy) head from the column. Then punch the intermediate shaft. It's not easy.


I learned my lesson. I have a big mill for such tasks now and I leave my pm-25mv equivalent for drilling, reaming, threading, milling with small end mills (up to 10mm), counter boring etc. I do use a boring head with this small mill, but I'm extra careful every time. And when running interrupted cuts I prefer to set it on high gear so there is less torque to potentially shear off teeth.

 

[WobblyHand]

My PM-25MV uses belts to the spindle. No gear teeth to shear. When using a large diameter cutter I find that it is imperative to use the low speed range, otherwise the motor stalls. This is especially true at the low speeds required for the cutter. My experience is primarily with HSS slitting saw blades. I'd like to make some pulleys to drop the speed further, to get the motor in it's sweet spot, but there's not much room for bigger pulleys. One of those round tuit projects.

 

[Flynth]

My PM-25MV uses belts to the spindle. No gear teeth to shear. When using a large diameter cutter I find that it is imperative to use the low speed range, otherwise the motor stalls. This is especially true at the low speeds required for the cutter. My experience is primarily with HSS slitting saw blades. I'd like to make some pulleys to drop the speed further, to get the motor in it's sweet spot, but there's not much room for bigger pulleys. One of those round tuit projects.

Did you mod it, or was it like that from the start? Perhaps the belt was PM's request to the manufacturer. If you search for PM-25MV you see pictures of a machine sold under a lot of names. My mill looks exactly like that, but it has a different name. The motor has a bronze(yellow metal) gear that meshes with a gear on top of the intermediate shaft (this is on top of the head and easily accessible). Then further inside the head there is this two-speed plastic gear that is moved by a dial on the side of the head. It meshes with one of two gears on the spindle.

I imagine the only place one can swap a belt in would be the very top where the motor drives the intermediate shaft. If so, is the two speed gear still plastic? Or is it metal? Perhaps the belt is enough to protect the teeth.

Edit: Actually nevermind... I found better pictures and it seems the similarities are external only. The PM mill has no speed selector and uses direct belt drive. This must be a superior system for using large cutters with interrupted cuts.