A few questions about end mills

[djh82uk]

Hiya guys

Ok, ive had my mill for a few months, though I was limited by the 4000rpm spindle, i now have an 800W 30krpm Kress.

Im wondering, what are the difference between the diamond pattern end mills (spiky) and the normal 2/3/4 flute end mills, what are the best uses for each?

I am assuming that the diamond pattern mills give a cleaner cut but cut at a slower speed due to not being able to get rid of the waste material quick enough, correct?

Also what are the formulas for working out what my ipm should be when cutting, based on RPM, and how to work out depth of cut etc.

Also how do I work it out for the diamond pattern bits?

Also any advice in general?


Also with my kress, i have a 3.175mm collet, now all my endmills are fine, except for these 0.125" endmills i have, they are twice as long as the others (which comes in handy), but for some reason, either the collet nut is too lose and they push up inside the chuck, or if i really tighten it, they push themselves out, causing a very deep cut before they snap, it's like they work their way down very quickly but stay tight in the collet, could it be they are a fraction thinner?

I just cannot make sense of it

Thanks

DJH

[LongRat]

By diamond pattern I guess you mean the cross-cut carbide cutters you can get? I think these are best in fibrous materials and generally things that form dust rather than curled chips. I have found them excellent in fibreglass and carbon fibre. Also just cut some obechi wood with good results. This style of cutter is also used in dentistry for finishing tooth preparations (dentine and enamel do not form continuous curled chips either).

[djh82uk]

Hiya

yes as in this type:

http://cgi.ebay.co.uk/Jinzhou-PCB-Ca...QQcmdZViewItem

Hmm, so how do I work out what to use on aluminium?

DJH

[Oldmanandhistoy]

Look for slot drills (two flute) ideally SC up to 12mm (HSS is ok for anything over 12mm). If you are looking for small end mills/slot drills I believe you will find what you are looking for on the link I gave you in another thread. If they have a TicN (Tin coating is not good for Ali) coating all the better.

John

[djh82uk]

Thanks

What sort of cutting bits do you think is the max i can use with my 800W kress and Taig (340 oz/in steppers), I just don't want to buy bits I cannot use efficiently, im thinking around 5mm diameter?

remembering my taig is sturdy but small, and nothing compared to the bigger machines obviously.

It's just i have to buy the collets etc for it to, so want to make the right choice

DJH

[djh82uk]

also the link you gave me only sells end mills upto 3mm

any idea where I can get cheap end mills in the uk of various sizes? im happy with reground items while i am still learning.

1/4" end mills I would like to try on some of my aluminium

Also any ideas on why a certain brand of end mills keep moving further out of the collet and cutting right through the workpiece?

DJH

[handlewanker]

Hi all, one of the first things you realise when working with collets is that there is no substitute for surface area when applying gripping force or expecting accuracy of rotation and concentricity.
The one size fitzall is a the biggest compromise that machine suppliers have tried to dupe the engineering community into accepting.

I've seen some people using one size collets, that is for example a 1/2" R8 collet to grip a cutter that is not quite 1/2", probably 12mm, but trying to squeeze a 1/2" collet down to grip 12mm is asking the collet to close out of round and out of parallel by .030".

You can do this with ER collets for all sizes from 3mm (1/8") up to 26mm (1") in the ER40 series, because they are multi slotted and are designed to do this, so will close to allow a 1mm variation in diam from unclamped size to 1mm below this and still maintain parallelity.

However if you have a collet that is a dedicated size, like the R8 Bridgeport type, then it will only fit that size and anything under will just get minimal contact at the end and also have run out.

The other most important thing to know is that when a collet is made it is sized in the CLOSED position and is parellel, so that it will open up to release the cutter when the drawbar or closer releases the gripping force.

A collet should have the size marked on it, otherwise the designed diameter is anybody's guess.
Anyone applying excessive force to make a collet grip had better check the designed size or the condition, as nothing slips like a worn or soft collet.

I have found that in the smaller sizes a holder having a parallel bore to the cutter size with a grub screw to one side will be superior to a cheap poorly made or worn collet anytime.
Ian.

[djh82uk]

Hiya

well the collet is for 1/8" bits, while the bits are 1/8" shank, tho they were cheap imports, so I guess the tolerances may not be the same, and thy could a be a fraction too small etc.

DJH

[afmcorp]

Originally Posted by djh82uk Hiya yes as in this type: http://cgi.ebay.co.uk/Jinzhou-PCB-Ca...QQcmdZViewItem Hmm, so how do I work out what to use on aluminium? DJH

they only thing i can see with a router bit of this pattern is plugging it up and either burning the work or breaking the bit. if it was something i was doing in aluminum i'd work with an endmill and lots of air flow to keep the mill clean. ur trying to keep the flutes from packing. i'm not telling u that u can't use them i'm only saying that my experience here is when i'm on aluminum big flutes pack chips so how can a small pocket not pack up. aluminum is sticky. if u can get a bunch of coolant with pressure on the bit that may also work. all i've done is use massive amounts of air.

good luck

[LongRat]

I agree, the cross-cut style of cutter is useless in aluminium. It is far too ductile and soft. You need larger flute clearance for this, which you will get with 2-flute milling cutters. Those diamond pattern cutters are designed for fibreglass sheet PCB material and do work very well for that application.
Regarding your slipping problem, first of all measure the shank diameters of your cutters to see what you actually have (rather than what they say they are). It could be that you have an imperial conversion of a metric shank (i.e. 1/8" = 3mm).

[hutchison]

Originally Posted by djh82uk also the link you gave me only sells end mills upto 3mm any idea where I can get cheap end mills in the uk of various sizes? im happy with reground items while i am still learning. 1/4" end mills I would like to try on some of my aluminium Also any ideas on why a certain brand of end mills keep moving further out of the collet and cutting right through the workpiece? DJH

try j&L industrial in the u.k, good range of general machining equip. call 0800663355 get them to send a catalogue. how are you tightening your collet nut?.
perhaps try carefully cutting a cylindrical groove or two around your tool shank at top and bottom so the collet will bite into it a bit more and increase the resistance of it pulling out, and perhaps just one axial groove running parrallel with the shank to help it stop spinning in the collet, failing that you could try a diamond type pattern, experiment!. have you got a photo of the spindle nose and collets?

[afmcorp]

well an endmill slipping out of a collet is directly related to how much force the collet is making against the shank. the more shank inserted the more force with the same torque. what u haven't said is how tight r u tightening the collet. if ur end mill is only say .250 inches 6+ mm u have quite a bit of collet material making the collet stronger and able to take more torque. this is say versus a 3/4" shank. i run DA180 here and i've seen the guys literally break up a 3/4" collet due to over tightening. there is not enough material left in the collet to withstand the force. so.... might i suggest using a bit more torque on the collet nut. also as someone stated earlier double check the actual diameter of the shank. i've seen some cheap china end mills come in here and actually be .030 undersized. the da180 are only good for a minus .015. so on that .030 u would not be able to apply the needed force on the face of the shank.

also if u are running a super high helix say 60 deg stop and try an endmill made for aluminum of about 30 degrees. this will eliminate quite a bit of the pulling down action. i might just do that anyway. some std mills run about 45 which may be too much for ur application. u might want to check into 3 flute endmills for aluminum. also note that i run an .125 [1/8"] endmill at 1300 rpm at 1.4 ipm giving me a .0003 / load per tooth at 80 sfpm. this is for 12L14 soft steel.

i also suggest u go to niagara cutter do a google. they have a complete cutting program so u can figure out where to start.

good luck