My first ever attempt at milling

[tmuir]

As I've never used a milling machine before I wanted to do something simple and cheap in case I messed it up so I settled on making myself some T-Nuts.

All marked out.

First pass done.

First pass with the swarf brushed off.

Half way through the final pass.

Finished surface.

My thoughts after my first attempt at milling.
It's not as noisy or scary as I thought it would be. :big:
Preparation is everything.
I can see me fitting a DRO to this soon.
I now fully understand why people motorise the X axis, winding is tedious to say the least.

Unfortunately bolstered with my success I started on the other side and on the second pass I wound too fast and the endmill bit in and broke, as this is the only endmill I have that's my milling finished for the long weekend.

Not how I wanted it to end but it was a good learning experience anyway.

 

[Brian Rupnow]

Were you climb milling when you did the other side?

 

[Cedge]

Brian
That was my first thought too. I killed off several end mills before it became natural to spot when I was climb milling.

Tony...
Milling was initially intimidating to me too. Now I seem to gravitate to the mill for mos things. Funny thing... I too expected the mill the be a bit more "violent" the first time I powered into metal. The power feed is definitely a plus and the one offered for the mini mill, by LMS works quite well.

The mods I made to mine that made the experience most enjoyable were the power feed, the belt drive, the collets and the extended Z rack. All were well worth the investment.

Now.... about that climbing cut....(grin)

Steve

 

[tmuir]

Were you climb milling when you did the other side?

No, well atleast I don't think so.

The front side was cut with the tool going away from me and the back side with the tool coming toward me which as I understand is the correct way to do it.
I was only using a 7mm end mill and I just think I fed too fast with it.
If a $15 tool has taught me to pay closer attention to what speed I feed at it was worth it.

 

[Lew Hartswick]

Yea. For that kind of a job I'd be using at least a 1/2" (12 0r 13MM) cutter.
Maybe even a 3/4" one. 4 flute for sure.
The cutter dosent travel the table moves. "push the material into the cutter"
...lew...

 

[cfellows]

I'm no expert by any means, so somebody correct me if I'm wrong, but, based on your picture, it seems to me that you were taking a pretty big bite out of that bar in one pass. I usually limit the depth to about .050" per pass in steel.

Chuck

 

[tmuir]

The cut was 2mm across and 5mm deep

 

[Brian Rupnow]

The cut was 2mm across and 5mm deep

That is a MASSIVE cut for a small machine with a small endmill. No wonder it broke.

 

[kvom]

I have been taught that the max cut in aluminum is 1/4 the diameter of the mill, and less as the hardness increases. So in steel with a 7mm endmill a 1mm cut is probably a reasonable bite.

You should also calculate SFM. For HSS cutter in CRS a value of 80-120 is good, so your spindle ought to be around 800-1200 with a 7mm endmill. It's hard to determine feed rate manually, but if the swarf is blue then you're going too fast.

 

[tmuir]

Did have the speed in the vicinity of 800 RPM, no rpm meter on my mill so set the dial at around 3/4 on low speed which maxes out at 1100RPM so had to be close to 800RPM as I had worked the speed out to be around 750RPM.

My book said 1/3 of diameter of endmill so I took that as 2mm would be ok.

I will be ordering a couple of endmills of larger diameter and will take shallower cuts

 

[Cedge]

Tony
After studying the photos, I believe you were indeed probably making climbing cuts. With the cutter at the far end ( as pictured ) you should be cutting back toward the camera. On the back side you'd want to cut going away from the camera.

You want the cutting edge of the end mill to enter the metal like a shovel would enter a pile of sand... along the bottom of the cut rather than pulling fresh metal back toward it.

Steve

 

[steam mad]

I was told, right or wrong I am not sure, that the feed rate should be 1 thou per tooth on cutter by speed of cutter = feed rate per minute. I use this formula with no problems.
i.e. 4 teeth on cutter = 4 thou
RPM 750 x 4 = 3000 thou per min. or 3" per minute feed rate.
This feed speed would be for the maximum cut the size of cutter is recommended for on material being milled.
With a lighter cut then faster feed rate.
This is what I was told anyway. ;D

 

[kvom]

That 3ipm feed rate calculation agrees with my textbook. Assuming your table advances .1" per revolution of the crank that's 30 turns/minute or 2 seconds per turn. I suppose you could get close by estimating a 2-seocnd interval for each turn of the crank.

 

[tel]

Yes, if the cutter ended up where it is shown after the cut in the first two pics you were climb milling.

 

[SBWHART]

Hi Tony

Easy way to remember if your milling the correct way is to think of a pile of snow or coal, shuffeling the pile from the bottom is OK shuffeling it from the top is bad Ie your climb shuffeling.

Tip for the T bolts burr the bottom of the threads over to stop the bolt comming through if it does it acts as a jack and can seriously damage your T slots.

Stew

 

[Tin Falcon]

Tip for the T bolts burr the bottom of the threads over to stop the bolt comming through if it does it acts as a jack and can seriously damage your T slots.

The other options are just do not tap all the way through just leave the last couple of threads semi finished.
The other option is use short bolts that do not bottom out.
Tin

 

[tel]

For conventional milling, the table (and workpiece) should move thus;

 

[seagar]

Hi Tony,I had never even seen a vertical mill used untill I purchased my mini mill,so to learne how to use it I decided to make a JinggleBell engine I found on www.npmccabe.tripod.com ( free download) as it is made mostly on the mill.Much to my suprise it runs.I have not done any clean up or bling so as to show my first attempt at building an engine.

IMG]http://i210.photobucket.com/albums

Ian (seagar)

 

[putputman]

I have always used a conventional cut for stock removal and leave a few thousands for a final climb cut. A light climb cut will generally give you a better finish. I find this is true with most materials also.
Does anyone else find this works for them?

 

[cfellows]

I have always used a conventional cut for stock removal and leave a few thousands for a final climb cut. A light climb cut will generally give you a better finish. I find this is true with most materials also.
Does anyone else find this works for them?

I do the same. Make one last, very light pass, doing a climb cut.

Chuck