Proper mill cutter and technique

[Megar arc 5040dd]

I made the pictured piece today to finish up my quill dro and struggled more than I should have. I very rarely have had to make pieces with a large cut out like this but have struggled when I do. I am wondering both what the proper cutter to use is as well as the proper technique. Or I guess maybe the easiest way or quickest way to do it. The material is .375" aluminum. The red line is the first cut I did with a .750 2 flute end mill. The depth of cut was the full .375". This took some playing with the speeds and my feed rate to get it to make the cut without it sounding bad but I got there. The next cut I tried to do was the blue line. At first I tried to step over .350" but it didn't like that and you could see it try to lift the part ever so slightly, I assume because so much material was gone. The part was in the vice 90 degrees from the way it is in the photo. This ended up being a good thing because I miss read the final dimension of the cut out and would have blown the part if it was able to make the cut. I reduced the step over to .150" and it made the cut but not nicely. The cutter wasn't a very sharp one I only used it hoping that the size would save me time. I swapped out the the cutter for a .500" 2 flute end mill that felt sharp. My selection of 2 flute cuter is very limited. I then tried the same thing again I believe at about .050" step over this time. it went ok but the cut looked crappy to. At this point I had about .050" left top take off each side. I decided to to 2 finishing passes climb milling the green line. The first one I did .025 step over and it looked just as crappy as before. At this point I switched to a sharp 4 flute end mill and did the same final pass climb milling with .025" step over and it cleaned up nice.

Should I have used a 4 flute end mill from the beginning? I was also thinking should I have used a much smaller cutter and just cut the U shaped perimeter? And if I did that should it have been at full depth of multiple passes at increasing depths? or should I have done what I did but not at the full .375" depth and done more passes at maybe .040" or .050"? Or did I do it the right way and it was just a case of using dull cutters? Previous times I have done similar pieces I have done it with a 12mm 4 flute carbide end mill and just slowly worked my way deeper and deeper. I was for a wrench for my collet chuck and was out of steel and took forever.

This seems like it should be a simple and fast operation.

 

[Martin w]

Nice job.
Do you have a band saw to remove most of the material first? That would help speed it up. Also gives you a small scrap piece to use in the future. I sometimes drill holes for the slots to remove some material.
I try to only use 2 flute endmills for aluminum. 2 flutes work well for machining slots though.
Martin

 

[Megar arc 5040dd]

Nice job.
Do you have a band saw to remove most of the material first? That would help speed it up. Also gives you a small scrap piece to use in the future. I sometimes drill holes for the slots to remove some material.
I try to only use 2 flute endmills for aluminum. 2 flutes work well for machining slots though.
Martin

I do have a bandsaw and that about using it but I wasn't sure how I would cut across the bottom once I had cut down the 2 sides. I'm not sure if it was the depth of cut or the cutter being dull or some combination of factors but I found that the 2 flute cutter didn't seem to cut as smooth. What I mean is not the finish wasn't smooth but the way it felt cutting. I guess the best way to describe it would be it felt like if a car had square wheels. Almost like you could feel when each flute came around and hit. I have very little experience with 2 flute cutters and all the ones I have are old used ones that came with my last mill. Do they normally feel this way?

 

[Martin w]

Kinda sounds like maybe you didn’t have your axis clamped tight enough? Do you have much play in your gib? Dull cutter will compound this also.

 

[ChazzC]

Mill model? And how were you holding the stock?

Re-enactment photos?

 

[Susquatch]

I echo Martin's recommendations but I'll add a few others.

In addition to cutting out chunks with a bandsaw, I also use annular cutters. They leave a nice round chunk of aluminum you can use as stock too. Great if you have a lathe. Just don't use the pilot unless you want a center hole.

I think many of the problems you describe are related to the lower strength of aluminium vs steel. I think the part is bending under the load of the cutter and perhaps the vise. I assume you optimized the speed N feed for Aluminium and your cutter. If not, you should do that.

I also think you cutter might be a bit big for your mill. You noted an improvement with a smaller endmill and that's probably why. As a general rule, I like 3/8 and 1/2 endmills for most milling work even on my big Bridgeport Clone. They are just happier tools!

Also, I'd avoid climb milling except when you have no other choice, and even then don't forget to lock the appropriate axis.

That's all I can think of without being there. I'm sure others will chime in with good advice too.

 

[Megar arc 5040dd]

Mill model? And how were you holding the stock?

Re-enactment photos?

I can take a photo tomorrow of how it was held. Basically if you turn the photo 90 degrees that was the orientation in the vise. Also I should mention that I was using parallels that in hind site where to tall. The piece was above the jaws, I was only clamping on about 3/16" of the 3/8" thick part. The mill is a Modern ZX45 (RF 45 clone). The bottom of the cut out is only .400" wide so it definitely could have been flexing both from the jaw pressure of the vise as well as from the cutter. This wasn't a critical part so I was trying a different way of doing it than I have done in the past in hopes of it going faster. I was only climb milling on the finish pass to try to get a better surface finish. On all the pieces I have been squaring up lately this normally works very well. That being said I have been doing it with a razor sharp 4 flute carbide endmill up until this time. I am not very efficient on the mill and it always seems to take me hours to do what looks like it should have taken a few minutes. Part of this is my fault for always trying to get every final dimension as close as I can to perfect even when it could be out by a country mile and still work.

 

[PeterT]

If you had in the vise like this (big blue arrows), its possible the part might be distorting a bit (little blue arrows). Now the only problem with gripping this particular part on Left/Right (in this view) is you cant mill the open C of the slot. It might be one of those cases where its better to clamp to a tooling plate with a sandwich of sacrificial material underneath & top clamps around the periphery. Its a bit more work to remove the ones you are cutting & then replace etc. but the part is always secure & in same position.

I agree with pre-cutting the chunk out with a saw or whatever (orange). Leave as little work for the end mill. And avoid having it cut on both sides (slot mode) when possible. The orange circles represent undersize through holes, same idea. You likely already have a layout with these center positions known, so you could just pre-drill them undersize. That just leaves a bit of cleanup milling to final dimension. You can even plunge straight down with EM in something like aluminum but may or may not be the optimal way depending on how close the dimensions & finish need to be on the connecting straights/tangent etc.

 

[trlvn]

... I am wondering both what the proper cutter to use is as well as the proper technique. Or I guess maybe the easiest way or quickest way to do it. The material is .375" aluminum. The red line is the first cut I did with a .750 2 flute end mill. The depth of cut was the full .375". ...

As usual, @PeterT has created a little diagram that illustrates very well the likely problem.

However, I have a related question: how big a cut is too big? Megar's RF-45 is probably a bit more capable than my RF-30 but a full 3/4" width by 3/8" depth seems like too much to me. (The LMS speeds and feeds calculator says the 3/4" cutter could be run at up to 1,020 RPM in AL.) I don't think our mills are rigid enough to cleanly remove that much material at once. With a 3/4" cutter, on an RF-45, I think I would have limited the cut to perhaps 0.100? And stayed away from the final positions by about 10 thous which I would then take with a cleanup pass at full depth.

For smaller mills, does anyone have a rule of thumb for the maximum amount of metal to remove in a single pass?

BTW, @Megar arc 5040dd were you using something for cutting lubricant? Common aluminum (esp. 6061) can stick to cutters which results in very poor surface quality. People seem to use WD-40, isopropyl alcohol or special purpose aluminum cutting fluid. I got some Relton A9 from BusyBee that seems to work well.

Quinn on the Blondihacks channel has done a number of videos on basic mill skills. I think she explains the concepts quite clearly and she uses an RF-45 mill so these may be a good fit:

Mill Skills

This is an educational series to help you learn to use your vertical milling machine. Watch them in order for best results! Satisfaction not guaranteed, espe...

www.youtube.com

Craig

 

[Megar arc 5040dd]

As usual, @PeterT has created a little diagram that illustrates very well the likely problem.

However, I have a related question: how big a cut is too big? Megar's RF-45 is probably a bit more capable than my RF-30 but a full 3/4" width by 3/8" depth seems like too much to me. (The LMS speeds and feeds calculator says the 3/4" cutter could be run at up to 1,020 RPM in AL.) I don't think our mills are rigid enough to cleanly remove that much material at once. With a 3/4" cutter, on an RF-45, I think I would have limited the cut to perhaps 0.100? And stayed away from the final positions by about 10 thous which I would then take with a cleanup pass at full depth.

For smaller mills, does anyone have a rule of thumb for the maximum amount of metal to remove in a single pass?

BTW, @Megar arc 5040dd were you using something for cutting lubricant? Common aluminum (esp. 6061) can stick to cutters which results in very poor surface quality. People seem to use WD-40, isopropyl alcohol or special purpose aluminum cutting fluid. I got some Relton A9 from BusyBee that seems to work well.

Quinn on the Blondihacks channel has done a number of videos on basic mill skills. I think she explains the concepts quite clearly and she uses an RF-45 mill so these may be a good fit:

Mill Skills

This is an educational series to help you learn to use your vertical milling machine. Watch them in order for best results! Satisfaction not guaranteed, espe...

www.youtube.com

Craig

I was using wd-40 but when I would spray a bit on, when using the 3/4" cutter it seemed to make the chatter worse. It looked like the chips would stick to the sides of the cut and not clear out. I stopped using the wd-40 and just held a light stream of compressed are on the cutter to clear away the chips and it cut better.

 

[Megar arc 5040dd]

If you had in the vise like this (big blue arrows), its possible the part might be distorting a bit (little blue arrows). Now the only problem with gripping this particular part on Left/Right (in this view) is you cant mill the open C of the slot. It might be one of those cases where its better to clamp to a tooling plate with a sandwich of sacrificial material underneath & top clamps around the periphery. Its a bit more work to remove the ones you are cutting & then replace etc. but the part is always secure & in same position.

I agree with pre-cutting the chunk out with a saw or whatever (orange). Leave as little work for the end mill. And avoid having it cut on both sides (slot mode) when possible. The orange circles represent undersize through holes, same idea. You likely already have a layout with these center positions known, so you could just pre-drill them undersize. That just leaves a bit of cleanup milling to final dimension. You can even plunge straight down with EM in something like aluminum but may or may not be the optimal way depending on how close the dimensions & finish need to be on the connecting straights/tangent etc.

View attachment 58383

Thanks for the really good advice. That is exactly how it was in the vise. I never thought of clamping it down instead of in the vise. It was just a squared up piece when I started so I just clamped it in the vise with out much thought. In the future I will make sure to spend more time thinking about alternatives to just using the vise. I will also pay more attention the the final shape and not just the starting shape of the material.

 

[Downwindtracker2]

I blundered on to a You Tube video, Joe Pie's I think, where he was making a fairly deep fixture out of aluminum. He plunge cut with a smaller diameter 2flute endmill to roughly the size, then he finished. He suggested 1/3 diameter nibbles. It was a lucky find for me, as I was milling a 5/8" aluminum plate to a 8" diameter for a mounting plate. It was to hold a 6" 4jaw on a rotary table. I used a 1/4" 2flute Long which I had to buy to get enough flute length . I also used it to finish which It did a crappy job of. That I attributed to both the operator and the mill.

 

[Megar arc 5040dd]

I blundered on to a You Tube video, Joe Pie's I think, where he was making a fairly deep fixture out of aluminum. He plunge cut with a smaller diameter 2flute endmill to roughly the size, then he finished. He suggested 1/3 diameter nibbles. It was a lucky find for me, as I was milling a 5/8" aluminum plate to a 8" diameter for a mounting plate. It was to hold a 6" 4jaw on a rotary table. I used a 1/4" 2flute Long which I had to buy to get enough flute length . I also used it to finish which It did a crappy job of. That I attributed to both the operator and the mill.

I will see if I can find that video. I find I do a lot of my learning from watching youtube videos. That said I am still a sucker for good old fashion books.

 

[kstrauss]

I agree completely with PeterT's suggestions. With 3/8-inch aluminum and heavy cuts the sides of the cutout will flex and lose grip when held in a vise as Megar-arc-5040dd described. The small piece of scrap is not large enough to be worth saving so remove most of it with you bandsaw and save the milling!

 

[Megar arc 5040dd]

This project has made me think of another beginner question. Are all 2 flute endmills center cutting or is that something to watch out for?

 

[PeterT]

The more pre-removal you can do with easier & quicker roughing tools (saw, drill..) the easier milling will be for finishing to dimension, especially with tougher materials like steel. Just need to pay attention to not paint yourself into a corner layout & orientation wise on the milling operation. Another lesson - watch out for pocket milling where you are going inside the periphery 9as opposed to progressively milling the entire pocket area). The last little bit when the inside chunk is becoming free can be a dangerous juncture because the EM can catch - jamming or throwing piece or breaking EM etc. I have used MDF backing boards for some setups for the EM to penetrate slightly or in this example, drill some extra holes for screws in to keep the pocket segment in place until milled out. MDF is pretty flat &inexpensive as a backing but be aware it can swell if soaked ie. cutting fluid.

 

[Downwindtracker2]

I am a heretic , which I prefer to call myself as free thinking. By design, a RF-45 should be a more rigid mill than a Bridgeport. Not as flexible or as handy, true. The bridgeports or clones that we can afford are usually well used. A quality new RF-45 might be a better option.The RF-45 are powered a heavy 2hp motors.Gearheads instead of belts. Of course, build quality to a price point comes into play. Or shall we say leaving some play?. Or in mine's case ,it was hard previous life.

 

[kstrauss]

No, not all two-flute are centre cutting. Why do you especially care? Do you plunge for the corners of the cutout and similar?

 

[jcdammeyer]

I would have done it this way. Not a full depth of cut but 0.1125 per pass. Leave 0.010" and then run the same profile again but with full depth of cut to clean up the edge.

 

[Tom O]

Did you snug up your locks? That can make a difference.