Ok, Rookie Here-- What Am I Doing Wrong?

[Bob V]

Hi,
I got my old Van Norman Mill about a week ago and have spent time until today cleaning it, changing sump oils, reducing backlash etc. Basically getting accustomed to the machine and tuning it up per the Manuel.

Today I bit the bullet and made my first cuts. I clamped down a piece of 1/2 inch steel bar stock (mild steel, I don't know the exact number or hardness). The Speed and Feed, as best I could tell, suggested an RPM of about 650 for the 1/2 inch 4 flute HHS end cutter I had in a collett in the spindle. The feed rate was hard for me to deal with since the machine is currently pure manuel-- no motor feed--so I just tried to "make chips".
My first two cuts across this 4" steel bar were only about 1/16 inch deep and seemed to go fine.
So I cranked the table up for a 1/8 inch depth cut and this went pretty well, but the tool started 'smoking" a bit-- so I used a little foaming cutting oil-- but this didn't seem to stick around long enough to help-- I made it across the 4 inches OK.
I had read that a cutter should be able to cut about half of the cutter diameter-- so I cranked the table up so the cut would be about 1/4 inch deep. This didn't go very well. I made it about a half inch into the material and the tool was smoking quite a bit and intermittently was spinning inside the collett--so I stopped. I tightened the draw bar to incease the collett hold on the tool, but it was already prettty tight- so I didn't think this was the problem.

What am I doing wrong. Is the tool dull (got it with the mill-- no visible chips under magnification. It's hard to say how fast I'm feeding the table. I don't want to go to slow (read that this make the tool "rub and overheat") and don't know if I was going to fast. Why is the tool spinning inside the collett-- I did clean light surface rust out of the collett then coated with WD40-- maybe too slippery? What's with this "smoking" is that expected if I don't have a high volume cooling system?

Sorry about the long post but I wanted to give as much info as possible.
Thanks in advance,
Bob

 

[JimDawson]

I suspect there are a couple of problems here. I think you are turning a bit fast for the conditions, maybe about one half that spindle speed to start with. I suspect that 650 would be the speed you might use with a new end mill under optimal cooling conditions.

It also sounds like the end mill was a bit dull to start with, and was further quickly dulled by over speed. It sounds like the end mill was not a good fit in the collet or the collet just was not tight. The collets should be clean and dry as should the end mill shank. There should also be a minimum of shank sticking out of the collet. Where possible, I normally have no more than about 1/8 inch of shank showing.

The smoking would be normal. With a little practice and experience, you will be able to feel and hear when things are just right.

 

[Bob V]

I suspect there are a couple of problems here. I think you are turning a bit fast for the conditions, maybe about one half that spindle speed to start with. I suspect that 650 would be thee speed you might use with a new end mill under optimal cooling conditions.

It also sounds like the end mill was a bit dull to start with, and was further quickly dulled by over speed. It sounds like the end mill was not a good fit in the collet or the collet just was not tight. The collets should be clean and dry as should the end mill shank. There should also be a minimum of shank sticking out of the collet. Where possible, I normally have no more than about 1/8 inch of shank showing.

The smoking would be normal. With a little practice and experience, you will be able to feel and hear when things are just right.

Thank's very much, Jim, I'll try half the spindle speed tomorrow. The end mill was well inside the collet-- only about 1/8-1/4" shank showing. But neither the tool or the collet were dry-- both had fine layer of residual wd40 from cleaning-- I'll clean both with brake cleaner so they grip better- how does that sound?
How do I tell the right speed to manually feed the table? Too slow, it rubs and dulls, too fast it dulls!
--Do you think I ruined the cutter with what I did?

 

[randyc]

I'm sure that this is a ridiculous question (it is prompted by the fact that you mentioned tightening up backlash) but you were conventional cutting - as opposed to climb cutting - right ? As Jim said, the spindle RPM is about right for a sharp 1/2 end mill.

BUT ..... using a small horizontal mill like yours and mine, I wouldn't dream of taking a 1/4 inch DOC in steel with a 1/2 diameter end mill. If I wanted to take off 1/4 inch of material in a single pass, I'd be setting up a three inch slab mill with the over-arm choked up as close to the work as I could get it and adjusting spindle speed accordingly.

Frankly, I just don't feel comfortable using a horizontal mill for end milling except for fairly light work. But this is ONLY a personal opinion based on limited experience

P.S. When manually feeding the table, a good indication of the correct feed is the sound that the cutter makes. A sort of "hissing" sound is good. Make sure that you're clearing the chips from the cut, too, re-cutting chips is not good for finish or for cutter.

You'll soon learn the ins and outs of your machine with a bit of practice. BTW, cutters for horizontal mills are still readily available and there are some great buys on eBay.

 

[Bob V]

I'm sure that this is a ridiculous question (it is prompted by the fact that you mentioned tightening up backlash) but you were conventional cutting - as opposed to climb cutting - right ? As Jim said, the spindle RPM is about right for a sharp 1/2 end mill.

BUT ..... using a small horizontal mill like yours and mine, I wouldn't dream of taking a 1/4 inch DOC in steel with a 1/2 diameter end mill. If I wanted to take off 1/4 inch of material in a single pass, I'd be setting up a three inch slab mill with the over-arm choked up as close to the work as I could get it and adjusting spindle speed accordingly.

Frankly, I just don't feel comfortable using a horizontal mill for end milling except for fairly light work. But this is ONLY a personal opinion based on limited experience

Randy,
Not a ridiculous question--but I managed to remember not to climb mill. My machine is a vertical mill that can be turned horizontal by rotating the head.
I don't think the Van Norman 16 is a "small mill" -- but maybe that's just my ignorance! --it's 2500 pounds of steel-- is that "small"?

 

[randyc]

Randy,
Not a ridiculous question--but I managed to remember not to climb mill. My machine is a vertical mill that can be turned horizontal by rotating the head.
I don't think the Van Norman 16 is a "small mill" -- but maybe that's just my ignorance! --it's 2500 pounds of steel-- is that "small"?

Yep, for horizontal mills a ton of weight is a fairly small machine - that's roughly the same size as my Lietz (universal horizontal with detachable vertical head). Sorry about the misunderstanding regarding head orientation but that doesn't change my opinion that a 1/4 DOC in steel with a 1/2 end mill is bad ju-ju, even with very fine feed and coolant.

 

[JimDawson]

I really don't know how to put the proper hand feed rate into words, it's a feel. If it's cutting slivers off, it's probably OK.

Cleaning the collet and cutter with brake clean would be good.

A new, high quality, sharp cutter will have a razor edge and will cut your finger. Cutters will work long past razor sharp, but there is some point that they quit cutting and start rubbing, a dull knife will sort of still cut. Normally you will see a large burr on the edge of the cut when they are pretty dull, and the feed effort will increase dramatically. If the machine is stable enough and you have enough power you can take a cut the full diameter of the end mill, but more normal is around 0.4 diameter to keep the end mill from pulling into the work.

 

[Bob V]

Yep, for horizontal mills a ton of weight is a fairly small machine - that's roughly the same size as my Lietz (universal horizontal with detachable vertical head). Sorry about the misunderstanding regarding head orientation but that doesn't change my opinion that a 1/4 DOC in steel with a 1/2 end mill is bad ju-ju, even with very fine feed and coolant.

Thanks again, Randy,
So: slower spindle speed (about 300) , DRY tool and inside of collet, and maybe cuts 1/8" deep?
Do you guys think I already ruined the tool?

 

[Bob V]

I really don't know how to put the proper hand feed rate into words, it's a feel. If it's cutting slivers off, it's probably OK.

Cleaning the collet and cutter with brake clean would be good.

A new, high quality, sharp cutter will have a razor edge and will cut your finger. Cutters will work long past razor sharp, but there is some point that they quit cutting and start rubbing, a dull knife will sort of still cut. Normally you will see a large burr on the edge of the cut when they are pretty dull, and the feed effort will increase dramatically. If the machine is stable enough and you have enough power you can take a cut the full diameter of the end mill, but more normal is around 0.4 diameter to keep the end mill from pulling into the work.

Ok, thanks again. -So if I want to do a plunge into steel with this machine-- should I start with a 2 fluke, maybe 1/4 inch tool?

 

[randyc]

Thanks again, Randy,
So: slower spindle speed (about 300) , DRY tool and inside of collet, and maybe cuts 1/8" deep?
Do you guys think I already ruined the tool?

I'd defer to Jim for just about all of this but I'd speculate that your end mill is <ahem> not optimally configured at this point Dry cutting is OK if you have the means of clearing chips and keeping the cutter cool. This is my method - maybe not the best but seems to work.

It's just a small air valve and air wand attached to a magnetic base. I adjust the little air valve to obtain a trickle of shop air - just enough to clear the chips from the cutter. It's not good to blow chips all over the place, they tend to end up in places that later cause problems, LOL. The air obviously cools the cutter as well as clearing chips.

Not visible from this angle but a similar arrangement on the far side provides coolant spray through a wand directed toward the cutter from a reservoir and coolant pump. I rarely use it though - it's a mess and the coolant tends to get stinky after sitting in the reservoir for a few months.



P.S. Jim mentioned the resistance to feed increasing dramatically with a dull cutter. That's something that needs to be monitored, even when using power table feed. My personal practice is to introduce the cutter into the work by hand, then feed it by hand for a bit before engaging power feed.

I believe that it's also good practice to disengage the power feed occasionally and check cutting resistance by moving the table by hand. You'll learn by doing ... the "feel" and sound of the cutting process will provide feedback that tells you how the work is progressing