MadModder
The Shop => Tools => Topic started by: John Hill on March 13, 2011, 12:30:14 AM
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Having lubed and checked out the new mill I first used it to trim the T Nuts to fit the table. Then I thought I would try a few more tentative cuts.
Hmmmm.... obviously got a bit to learn, I do know enough to avoid climb milling but I seem to have destroyed the end of a 12mm endmill already, just on a bit of unidentified steel (incidently the little shaper had no trouble with this piece!) I tried to cut a slot 1mm deep with the spindle at 500rpm, it started OK but very soon it got really hot and when it spat out a couple of red sparks I called it a day on that little exercise.... :scratch: I thought this would be a basic milling operation?
With the end munted I tried a little cut along the side of 1/4" plate, thats more like it! A nice easy cut and a good finish.
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Hi John
You could be running at too high a speed, cutting speeds tend to be a bit slower than you would use on a lathe, you have an interupted cut so things tend to vibrate a bit more. Try again slowing things down and listen to the sound of the mill, youll soon lern to secognise a happy mill. :D
Stew
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Thanks Stew, there is just one slower speed on the mill so I will try that next time I go to the shop.
Meanwhile, having destroyed the end of the end mill I figured I had nothing to loose by trying to sharpen it.
First, I held the end of the tool against the side of a grinding wheel trying to get an end on it as near to square as possible.
The next step was really crude, I held the tool against the edge of the grinding wheel to grind a sort of cross between the flutes, the tool has four flutes.
At that point I had four tips but unlikely to be the same 'length'. I put the tool in the mill and held a small diamond lap flat on the top of the vice, started the spindle and gently lowered it onto the lap which I moved around a bit. My intention being to get all four tips to the same length.
Although the tips might have had the same length they had no relief so I blued them and with the tool in the vice carefully gave each tip a bit of relief being careful to leave a whisker of blue visible.
Then I tried it out!
On cast iron it went really well although with the centre ground out there was no way I could have expected to have drilled with it. It cut a nice channel in the cast so I tried it again on the steel, 30 seconds later I was back to square one!
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i had a boxed set of "coated" endmills and slot drills, on ally, worked very well, on any sort of steel, no joy
the coating can be scraped off very easily!!!
now gone to carbide :D
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John
The steel you are trying it on may have a hard skin you get this sometimes especialy if its cast steel, some steels also work harden as you cut it, try a bit of different steel.
Stew
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John
The steel you are trying it on may have a hard skin you get this sometimes especialy if its cast steel, some steels also work harden as you cut it, try a bit of different steel.
Stew
I am not sure it is hard, it just seems to not like being cut and gives gummy looking burrs, more tough than hard if that makes sense! :scratch:
I will try my 'sharpening' technique again tomorrow. :scratch:
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Hello John,
Welcome to the wonderful world of milling. :)
With respect trying to sharpen a 4 flute end mill (off hand) is a somewhat difficult task. I sometimes try to “touch them up” by using a “dremel” with the milling cutter firmly held.
I think that bit of steel is probably too hard and tough for your (HSS) cutter.
Seems your cutter went blunt very quickly – that tends to indicate the material you are trying to cut is “hard” or there was something very wrong with the cutter.
Dave
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FWIW I use carbide mills for steel cutting, finishing off with HSS if I need a better surface finish. Sometimes carbide can give quite good finishes depending on the steel. For the final finish cut(s) with HSS, only a shallow depth, say 10 thou or less.
I tried an HSS flycutter as per bogs design on steel but it repeatedly blunted very quickly. Swapped it out for a carbide indexable lathe tool I had lying around and it seems to last forever, with a superb mirror like finishes.
If you try to use HSS for lots of steel cutting you will get through a lot of cutters. However HSS is a lot more forgiving when you ding the cutter accidentally, and carbide one will break with a low level of abuse. HSS roughers are interesting to try with large material removal rates, and work well for soft metals.
As bogs says, richontools are a good source of mills, although the carbide ones seem to be imperial. I've just decided to retire my first 20mm HSS endmill from them so its lasted a good 6 months. 3/8 and 3/4 inch imperial carbide will fit 10 and 20mm ER collets.
Good luck with your future projects.
Best regards
picclock
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Cutting steel, I'd run a 12mm HSS endmill at about 350rpm tops, with plenty of cutting oil, and a relatively slow feed rate. I'd also only take fairly light cuts, maybe 10-20 thou, or less if taking cuts off the side.
IMHO, you need a roughing end mill; you can really attack steel with those - think 0.1" depth of cut, 500-1000rpm speed, and a respectable feed rate. I've never bought new ones, I've always got them off eBay or Apex. I've got about 50 of them now, and they're brilliant.
e.g. http://cgi.ebay.co.uk/320669523359 (http://cgi.ebay.co.uk/320669523359)
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I tried to cut a slot 1mm deep with the spindle at 500rpm, it started OK but very soon it got really hot and when it spat out a couple of red sparks I called it a day on that little exercise.... :scratch: I thought this would be a basic milling operation?
With the end munted I tried a little cut along the side of 1/4" plate, thats more like it! A nice easy cut and a good finish.
End mills 4 flute work best for profiling as you found out and Slot drills for slots 2 flute there are 3 flute cutters that seem to do both quite well, I have a few throwaway FC3
In steel, either cold or hot rolled I use 1/2" cutter at 500 rpm as a guide then a 1/4" at 1000 rpm 1/8" 2000, cutters need to cut so don't baby it if the cutter is just rubbing it'll dull quick.
this picture is from a model engineering book so takes into account of the rigidity of smaller machines so a 12mm cutter could cut 12mm deep and 3mm wide sounds a lot but I've tried it and with a little bit of backing of from the max it works.
Edit.. my machine has a 40 taper I think yours is an R8 ? either way just try upping it till one of you complains :dremel:
http://bbs.homeshopmachinist.net/showthread.php?t=46150 post 5 is by Teenut he's talking about big machines here but it'll give you an idea.
Lee
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I've been using G-Wizard feed and speed calculator lately. I plugged in a 12mm 4-flute HSS endmill cutting a slot .01" deep; it shows 867 RPM and 3.7 IPM in CRS. So I don't think your 500 RPM was the problem. It seems more likely that the mystery steel is a lot harder.
The color of the chips is a good indicator; if they're blue it's likely too fast. Golden color seems to be just right.
Here's a pretty good online speed&feed calculator: http://www.whitney-tool.com/calculatorSpeedFeed.html (http://www.whitney-tool.com/calculatorSpeedFeed.html)
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Semi skilled has it right in the dia.
was you trying to cut full width cut of the end mill , think about it the edge of the end mill facing the direction on the cut would be just pushing
for speed I use for metric guide no for steel 25 therefore 25 *320 \cutter dis in mm = give me 666 rpm . ye gods that the mark of satan :doh: that mud have been the trouble :D
as a rule I use about a 1/3 cutter did for the depth and a 1/4 for the width
above all DO NOT let the cutter rub get the travel speed up to get a good chip load as Kvom said chips should be at the hottest light straw at the most
As you have found out end mills cut best on the sides :D
a little bodge with a dull cutter with no t/c available is just to tip the corners ( leading edge ) to about 45 deg by a few thou keeps it cutting but will not make a sharp corner any more
Stuart
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I would take a hacksaw to it and see if it cuts or if it just bounces off the workpiece. If it bounces off, I would use it as a doorstop.
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John, a couple of thoughts...
Is it perhaps possible that that unidentified piece of steel might be stainless steel ? - that will cause you a bit of grief with milling if the speed is too high, as it will work-harden rapidly if you're going at too fast a spindle speed, or too low a rate of feed.
Have you checked your mill's spindle pre-tension adjustment since taking delivery? - I had similar problems last year when I bought my mill, and adjusting the spindle really helped to get better finishes and ruin less cutters.
Regards, Arnold
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Thanks, lots of stuff to think about there and I will examine those links. I will perservere with the HSS for a while yet until I can explore just what the practical limits are, my bit of scrap steel is not exactly hard but it does not 'machine easy' either. I used pieces of the same stuff to get acquainted with my little shaper and initially I made very slow progress there too until I got tool sharpening and feeds etc sorted but it eventually handled it OK.
Rubbing, yes that is what happens after a minute or two. Keeping a constant feed rate with the 'X' handles will be a challenge and I can already see why so many people go for the power feed, maybe me too, but not just yet!
I have been pondering the shape of the end mill and can see it would be very difficult (impossible?) to sharpen one entirely free hand, no wonder I see so many projects to make tool and cutter grinders! But really it does not look too hard to make a jig or two to sharpen just the ends of flutes, grinding the centre to keep the plunge capability is another matter however!
Although this experience with steel has not gone as I imagined it would I am really pleased at how easy it is to work cast iron, hmmmmmm...... now I need a source of old cast iron. :scratch:
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No Arnold it is not stainless but it may be work hardening. :scratch:
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John, from my limited experience other steels with a higher carbon content (like silver steel) will work harden as well, so that is a distinct possibility.
When I get this type of scenario, I slow the spindle speed down as low as it will go, and then take a positive feeding cut; I want to see a chip coming off of each flute of the cutter. Not a big chip, but a chip none-the less, otherwise things are rubbing and will just ruin the cutter and if it's a work-hardening metal make things worse. Takes a bit more time to do, but is a lot cheaper!
:) Cast iron is a really nice metal to machine if you don't get inclusions and "frozen" spots. Makes a wee bit of a mess and you end up with black hands, face and tools, and an iron taste in the mouth, but a lot of fun none-the-less. I love the stuff but it's a bit hard to come by here, and expensive!
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John,
When I first started using a mill I destroyed a fair number of end mills including solid carbide. After I had accumulated a drawer full I decided it was time to try my hand at sharpening them. I bought the sharpening fixture that everyone sells for around $40 USD only to find that it was designed to use on a surface grinder with a magnetic chuck. Not having such a machine I proceeded with Plan "B". Using a cobalt drill, I drilled holes so I could clamp the fixture to my mill table. Then I made clamps to fit in the holes. The first set of clamps were too narrow for the tee slots of my new mill so I am in the process of making new ones. I now am able, using a cupped grinding wheel, to resharpen all my inventory. I recently bought a diamond encrusted cup wheel for sharpening carbide.
Here is what my fixture it looks like.
(http://i944.photobucket.com/albums/ad289/AlveyJoe/100_2638.jpg)
(http://i944.photobucket.com/albums/ad289/AlveyJoe/100_2641.jpg)
(http://i944.photobucket.com/albums/ad289/AlveyJoe/100_2643.jpg)
Joe
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Cast iron is real easy to machine, like butter.
Apart from the actual steels a lot depends on the cutter. For me false economy buying the cheap stuff but cant stomach the prices of the good stuff.
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G.Day John,join the Q with your new Milling Machine.
One of the problems is human nature,that is you are told not to do something but not informed as to why?
Books on machining will tell you "do not use 4 cutter end mills to cut slots" Why?
Well to try to explain here would take up too much space but try to imanagin what is happening when using a 4 cutter mill.
The mill is revolving in one direction at a certain revolution.
The material being cut is traveling in a certain direction at a certain velocity and depth.
Now take a look at the tooth that is in the leading position.
It is causing the work to go over to the opposite side and will make the cutter go the other way causing the two cutters that are now cutting the sides to cut larger than their dimention.
This causes the slot that you are cutting to be larger than the dia. of the chosen cutter also ragged sides will be made.
Always use a good Suds Coolant/Lubrication fluid,and enough of it.
Also i bet that the time that the mill cutter brakes is when you come to the end and about to free it self from the cutting.
This is the most dangerous time of the whole operation as the cutting teeth are asked to cut large chunks of metal and if you have not tightened your gibs then the slack is also taken up causing more metal to be offered up to the cutter.
Most of us mill at too low a speed causing the cutter to take on too much at every revolution,think about it.
I would not use a new milling cutter on Ferous metals but would keep it for use on Brass or Ally first,then when the edge has worn off then use on Steel etc.
Good luck with your new toy,
GerryB