Rotary Table Radius Chatter

[hfguy]

I'm a novice attempting to make a radius channel in a flywheel. Mill is a HF bench top mill/drill. Inexpensive imported 4" rotary table but with slack adjusted out, with home made but sturdy adapter plate to mount 3" 3 jaw chuck on to rotary table. Everything securely mounted, bolted, tightened, locked. X, Y locked. Cheap import 4 flute end mills. Before I start milling, I check for any play anywhere.

Trying to make radius channel in small, 2 1/2" round steel blank.

I get significant chatter no matter what I try. Tried different mills, including new ones, different sized mills, different feed rates, different cutting depths. It's chatter city no matter what I try.

What am I doing wrong?

 

[ShopShoe]

"Cheap import 4 flute end mills."

Asssuming you've got everything tight and you are feeding slowly and taking small cuts, I would try for higher-quality 2-flute end mills.

What steel are you cutting? Some are easier than others.

Try locking Z, cutting, going deeper, locking Z, cutting, etc.

After that, I would start checking for problems with setup and rigidity again. I fought all those things when I was starting: It's surprising what you find when you keep looking.

Best wishes for success, and let us know what works (something will).

--ShopShoe

 

[Arnak]

Hi hfguy,

Try lowering the cutter speed, chatter is usually down to rigidity and speed.

See here :-

https://www.kennametal.com/en/resources/tech-tips/milling/tech-tip-32.html

I hope you solve the problem.

Martin

 

[hfguy]

Thanks guys. I'm trying to mill 1018 steel. Also, I am locking Z also. I'm thinking maybe I need a high quality mill bit. I'll try a high quality 2 flute.

 

[bazmak]

How wide and deep is the slot? Are you plunge cutting to start and what size
cut are you trying to make.Ie width and depth.I would drill a slightly smaller hole to start with as the entry point for the plunge cut and use a smaller
carbide 2 flute cutter.Then finish with with to size cutter.Dont forget size of the mill plays an important part in ilimminating chatter

 

[kuhncw]

In the future, you might switch to 12L14 free machining steel or maybe 1144. Both machine nicer than 1018. This is probably not your problem, but it will make life easier in the future.

Chuck

 

[hfguy]

Thanks for all the input guys. I've ordered this cutter and will try with very shallow cuts and drill starter hole first. I'm stuck with the 1018 for now. As soon as the new bit comes, I'll post an update. Love you Amazon Prime.



Niagara Cutter N64068 High Speed Steel Square Nose End Mill, Stub Length, TiN Finish, Roughing/Finishing Cut, 35-Degree Helix, 2-Flute, 2" Overall Length, 0.188" Cut Diameter, 0.188" Shank Diameter

 

[Gordon]

Try tightening down the table lock so you can just rotate the table. I have one of those cheap tables also and the table lifts off from the base. Those tables can work but everything has to be as tight as possible and everything has to go slow.

 

[john_reese]

You might consider chain drilling before trying to mill. A drill will remove metal faster than a mill. Just make sure the drill is smaller than the intended channel so there is metal to clean up on both sides of the slot. With less metal for the milling cutter to remove I expect you have less tendency to chatter. I often chain drill a slot before I mill it.

 

[bazmak]

Looks like you want to cut a 3/16 dia or nom 5mm slot
Look on ebay,at that size you can get a no of solid carbide
2 tooth cutters,they cut well and last a lot longer than HSS
As previose comment,chain drilling is more labour intensive
but well worth the effort in steel. Good luck

 

[JackSimons]

I recently had a similar problem. I needed to tighten the gibs, and the gear mesh on the table. That did it for me. The table was old, and the previous owner "Cleaned it up". Good luck.

 

[Wizard69]

I'm a bit surprised athlete suggestions to go with 2 flute mills, I'd rather the you stayed with 4 flutes myself. Lower the spindle speed though.

As for tightness of everything that is debatable as many of the Chinese imports don't mate up part correctly. You need to make sure everything is well fitted on the mill and rotary table. This means properly fitted gibs on linear slides and a rotary table mechanism that properly mates up.

I might ask how does the mill work cutting the same material with the same tool without the rotary table. If the machine does better without the rotary then you have a couple of possibilities. The rotary table needs work. Or the hight of the rotary table gives the cutter enough leverage to hi light issues with the linear slides on the mill.

 

[hfguy]

Lots of promising suggestions. Thanks guys. I've fiddled with my mill gibbs a lot to get them as precise as I can. I've checked X and Y axis and for play as precisely as I'm capable given my tools, and there is no discernible play in the entire setup when I hold the X and Y and rotary table and try to move to check for any play.

I've not had any trouble using the cheap mills in making linear slots on my mill. However, I have to stress that I'm very inexperienced and don't have a lot of hours in front of my mill or lathe.

I like the idea of chain drilling and I'll try that. The new 2 flute HSS bit should be arriving in a day or two and I'll be trying that. If that doesn't work, I'll purchase a really good quality carbide 4 flute mill. Ugh. (I'm on a budget.)

 

[mcostello]

With a less than rigid setup the carbide end mill may chip. It might be better to get experience with cheaper tools. Are You climb milling or conventional milling? Climb milling sometimes makes a sketchy setup worse.

 

[hfguy]

Good question - climb or conventional. I've given that some thought as I'm cutting a channel in a radius. So it's really both climb milling and conventional milling I guess. I was thinking that perhaps that milling a channel is both, and that the inside radius cut is going at a different (slower) speed than the outside cut, that that may be a contributor to the chattering? Thoughts?

 

[Wizard69]

Good question - climb or conventional. I've given that some thought as I'm cutting a channel in a radius. So it's really both climb milling and conventional milling I guess. I was thinking that perhaps that milling a channel is both, and that the inside radius cut is going at a different (slower) speed than the outside cut, that that may be a contributor to the chattering? Thoughts?

It is hard to say, id consider lowering the depth of cut. If you still have chatter say after cutting the depth of cut in half then id have to say you have mechanical issues someplace in the machine. I wouldn't trust that rotary table actually. It is hard to tell without inspection but many of the Chinese imports are not fitted up well.

Do feel free to adjust spindle speeds to find the machines happy zone. Normally you would adjust downward but sometimes an increase in RPMs can move the machine out of the Zone where it easily chatters.

Other things to consider:

Keep the end mill as short as possible.

Lock all unused axis down tight. If you have too loch down all the gib bolts. This to try to turn the machine into one massive piece of cast iron.

If the column on the mill is a box section consider filling it with epoxy granite.

There are many end mill designs out there that try to address issues with surface finish, harmonics and the like. Sometimes the simple and cheap end mills just don't work well.

Avoid cutting channels with full size end mills. Cut under size and then clean up with a full depth cut on each wall.

As others have pointed out drilling is perhaps the most efficient thing you can do on these small mills. Chain drill and even consider cutting out much of the waste by hand.

Probably should have mentioned this before but make absolutely sure you aren't recutting chips. This is actually a huge issue as it not only induces vibration it can also ruin an end mill pretty quickly if the material works hardens at all. Chip evacuation is a huge issue on deeper slots.

Keep the cutter flooded with coolant.




In any event a lot of ideas thrown out to give you some possibilities.

 

[mcostello]

Could You go with a smaller end mill and use the correct size to finish?

 

[DJP]

I sometimes use tapping fluid (Tap-Magic) when the milling cutter needs some help. A few drops is all that it takes.

 

[arc]

Does your mill use a drill chuck or a collet to hold the end mill. If it is a drill chuck, that may be your problem.

 

[JackSimons]

If the chatter is in between the rotary table platter (top) and the body of the rotary table then tighten the gibs in the rotary table.