Machine marks while milling

[Philjoe5]

Last evening I milled a piece of steel of unknown alloy. I used an inexpensive but new end mill of 1” diameter. I obtained this surface finish, which, while appealing to the artist in me, seems fairly coarse. I was taking light cuts of maybe 0.020” at not more than 200-300 rpm. I did not experience any unusual vibration during this operation.

A few days ago I milled some 7000 series aluminum using the same setup and obtained a surface that’s quite smooth

Am I seeing the consequence of a steel alloy that doesn’t machine well or might there be some machine issues I should check? Any comments or advice appreciated,

Cheers,
Phil

 

[steamer]

Hi Phil,

First blush your spindle is not square to the table. The cross hatches will be at right angles if it is. The heal of the cutter is cutting deeper on one side than the other

If the feed was left to right in the first picture, then the head is off in the front to back position.



I would slow the feed down a bit...quite a bit. Perhaps also run your speed up.

That should help

Cutting speed with HSS cutter for mild steel is 100-125 FPM or there abouts

That works out to about 400 rpm for a 1" cutter

CRS leaves a nicer finish than HRS, but is less dimensionally stable

But getting the head trammed is important.

 

[Holescreek]

Phil, I am not seeing the same thing Steamer is. I see even markings made by both the leading and trailing edges of the cutter. This would indicate that the head is trammed in. You didn't say what type of mill which would determine how heavy the table is. At best, it would be a speed/feed issue as Steamer pointed out. At worst, the table gibb could be a bit too loose allowing lift on the harder material.

Sometimes the inexpensive cutters also come with burrs on the corners as well, but that wouldn't explain the entire surface. Check your gibbs for excessive play, speed up the cutter and try it again. -Mike

 

[Philjoe5]

Mike, Steamer,
Thanks for the advice. The mill is an X3, about 200 kg. Checking now, I can see that the "z" axis gib could use a slight tightening. That's easiest to do, but I'll check the tramming too.

Cheers,
Phil

 

[Mainer]

Lock all the axes (including Z) that you aren't actively moving. That may help, but I suspect that it's mostly due to the combination of speed/feed/material you have. I agree that slightly higher RPMs may help.

And, it may be the material you're dealing with. Some stuff is difficult to get a good finish on, no matter what you do.

 

[joeby]

Could be too slow spindle speed, or you're feeding too heavy. If you're on a light finish pass, you can speed up the spindle a little. The spindle tram looks ok to me.

If you're using cheaper end mills or re-grinds, you'll see that when one flute is higher than the other(s). That happens when the grinder keeps starting on the same flute and grinding wheel wear causes the last flute to be higher than the rest. Not so much an issue anymore though.

Could also be runout of the spindle/collet.

Just a few thoughts.

Kevin

 

[Rustkolector]

I have an X3 also. I have seen this pattern on mine, and it turned out to be due to a poorly ground import end mill. I have learned at least three different times, that most of those "on sale" import end mills are only good for Delrin. I'm a slow learner. A very light cut with a 3" wide flycutter on a piece of aluminum would quickly tell you whether your mill needs tramming. Mine did. The leading an trailing cuts should be very even and very smooth.
Jeff

 

[steamer]

You might be right Holescreek....pictures and my monitor can be misleading....

Lets see what we find......Jeff's right...a light cut with a flycutter will point out a tramming issue.

Dave

 

[Maryak]

Looks to me like something was loose.

Draw bar

Collet chuck

Collet

Mill head

Table jibs.

Vice/Clamps

Is the cutter blunt now?

Best Regards
Bob

 

[Philjoe5]

Ok, I had a little slack to take up in the “z” axis gib, which I did. When I checked the spindle alignment I noted I was +0.003” on the left side of the table and – 0.003” on the right side as measured at 8 inches on each side of the spindle.

I could reproduce these results over several trials. This was worse than I measured when I first set the machine up over a year ago so I suspect some settling may have occurred. I adjusted this to + 0.001 on one side and – 0.001” on the other. The dial indicator didn’t move going front to back on the "y" axis.

The next opportunity I have to machine some of that steel I have left over, I’ll report results back here. Thanks for the advice folks.

Bob, the cutter appears to be OK and I'll test it out on that next milling opportunity on that steel.

Cheers,
Phil

 

[Mike N]

Last evening I milled a piece of steel of unknown alloy. I used an inexpensive but new end mill of 1” diameter. I obtained this surface finish, which, while appealing to the artist in me, seems fairly coarse. I was taking light cuts of maybe 0.020” at not more than 200-300 rpm. I did not experience any unusual vibration during this operation.

A few days ago I milled some 7000 series aluminum using the same setup and obtained a surface that’s quite smooth

Am I seeing the consequence of a steel alloy that doesn’t machine well or might there be some machine issues I should check? Any comments or advice appreciated,

Cheers,
Phil

The spindle speed is to slow & your feedrate to fast! Are you using a 2 flute cutter?

 

[Philjoe5]

Mike,
I'm using a 4 flute centercutting end mill.

Cheers,
Phil

 

[Cedge]

Have to agree with Mike.... spindle is too slow and feed is too fast. The cross hatching seems to indicate the mill is very close to being properly trammed on the X axis, although it appears that it could be off just a wee bit on the Y axiz.

I intentionally made a similar cut while testing the power feed on my mill. As the test progressed, a faster spindle rotation and a slower feed rate made the marks almost invisible. the finish cut almost looked like a CD. As said before... a fly cutter will definitely tell the whole story much more clearly.

Steve

 

[steamer]

"A few days ago I milled some 7000 series aluminum using the same setup and obtained a surface that’s quite smooth "


Missed that line when I read it.....as I said the speed and feed are off for the steel part. Probably something loose also as was discussed.


Dave

 

[Julian]

Motorise your table so the feed is controlled. I have never got a good finish with large cutters until I went to cnc. I am not saying go to cnc but if you motorise the x table as per Firebirds post on Machine mods on this forum you will get a better finish. Part of the problem is the human arm and hand cannot turn a wheel at a constant smooth rate. It is natural that we move the wheel at different speeds on EVERY rotation especiall when the hand is moving downwards as gravity take charge. If you divide each rotation into four quadrants each will be a different speed....there is nothing you can do about it. Practise will improve it but not eliminate it. My cnc mill will take a 20mm 2 tip index cutter across with virtually no marks. By hand it is crap.

Julian

 

[Mike N]

Mike,
I'm using a 4 flute centercutting end mill.

Cheers,
Phil

I noticed you said you were using an inexpensive 1" 4 flute cutter. It looks like only one of the flutes is actually doing all the work! Similar to a single tool flycutter.

 

[Philjoe5]

Ok, I trammed the mill, adjusted gibs. Next, I got the same end mill and some of that steel I was having trouble milling. Based upon suggestions of slowing the feed rate and increasing spindle speed, here’s the result.

It may be hard to see from the picture but the finish is way better than before ;D ;D ;D. I believe my feed rate/spindle speed was part of the problem. Adjusting the mill probably helped too. I am quite gun shy about running the spindle speed too fast. Early on I went through a few end mills in short order by running them too fast (along with a fast feed rate).

I learned something new thanks to all your suggestions. This forum is great. I appreciate someone offering help on the basis of some pictures that are not all that clear.

Cheers,
Phil

 

[steamer]

Well what ever it was I am glad we could help! ;D

Happy machining!

In the questions catagory I have a post called "Resources for the Beginner"

It really should say for everybody.....in any case there is a wealth of information including feed and speed for various materials ( I think...I'll check and post a referance if there isn't)

More importantly how to calculate given the work and the cutter....

Dave