true flat bottom end mills

[Michael GilliganParticipant @michaelgilligan61133]

Michael Wiliams,

Many thanks for introducing the right terminology

I have been busy on Google, and just found this very useful eBook.

MichaelG.

[I.M. OUTAHEREParticipant @i-m-outahere]

Hi Olaf .

You may be able to use a side and face mill like the one below mounted on a stub mill arbor .

You would essentially be using it like a very thick slitting saw so the rigidity of your machine may be an issue and so could the type of material you are cutting ( looks like alluminium ).

This one is 2-1/4" x 1" x 7/16" x 14t but are available in many different dimensions and tooth count.

[blowlampParticipant @blowlamp]

Just had another thought.

Did you use a centre cutting endmill on the reel in the pictures?
I'm thinking that if you didn't, then that might account for the curvature.

Martin.

[jason udallParticipant @jasonudall57142]

Slot drill?

[Olaf KundrusParticipant @olafkundrus84366]

Yes I used a center cutting endmill, I ordered it special for this job an it was sold as slot drill because I thought a slot drill would have true flat bottom. But it looks like this one has not.

Olaf

[Tony Pratt 1Participant @tonypratt1]

Hi Olaf, no slot drill, endmill or similar will have a flat bottom. They are all "dished" on the end to allow for corner wear as the cutter is used.

Tony

[Harold Hall 1Participant @haroldhall1]

Olaf, I suspect you are working with the cutter central over the rotary table's axis, If so, the leading edge with be at a larger radius that the two sides of the cutter. You need the leading edge of the cutter to be in line with the rotary table's axis.

On the subject of a flat end end mill. For normal milling, such an end mill will just not work, If you would like me to explain I will. The concave, for better of another word, nature of an end mill is absolutely essential.

Harold

[Harold Hall 1Participant @haroldhall1]

Olaf, I suspect you are working with the cutter central over the rotary table's axis, If so, the leading edge with be at a larger radius that the two sides of the cutter. You need the leading edge of the cutter to be in line with the rotary table's axis.

On the subject of a flat end end mill. For normal milling, such an end mill will just not work, If you would like me to explain I will. The concave, for better of another word, nature of an end mill is absolutely essential.

I would have answered earlier but I have been off line for a few days due to a router failure

Harold

Edited By Harold Hall 1 on 15/09/2012 21:03:17

[Sub MandrelParticipant @submandrel]

> On the subject of a flat end end mill. For normal milling, such an end mill will just not work, If you would like me to explain I will.

Ironically, however, because Olaf is milling a cylindrical surface, the sgenerated shape itself provides the relief that would allow a flat ended cutter to work.

I agree with the d-bit suggestion, or even re-sharpening a blunt slot drill to be flat. Olaf, if you haven't got a becnch grinder but you do have a mill, you really ought to invest in one, it will pay for itself in re-sharpened cutters even if you only do simple things like grind old endmills into single point cutters.

Final thought, use a cutter less than haf the width of the slot. finish the slot with 10 or 15 overlapping passes – slow, but the end result will be flat for practical and cosmetic putposes.

Neil

Edited By Stub Mandrel on 15/09/2012 21:34:38

[Harold Hall 1Participant @haroldhall1]

Neil

My comments re standard end mills not working for normal milling if ground flat is a fact.

However, your comment about the curved surface I agree and made me have second thoughts. I have though looked at my sketch I drew and still say that if the cutter is central above the rotary tables axis it will produce a convex surface with a standard end mill or one ground flat. In this case the workpiece is rising into the cutter and I have made that mistake myself, it makes the rotary table harder to turn. I think Olaf is turning aluminium so it may not be that obvious…

What I failed to do was to draw out my suggestion of making the leading edge in line with the rotary table's axis, in this case it will only cut on the outer diameter like normal milling but will cut a concave surface as the outer edges of the cutter, being behind the axis, will be at a larger radius.

Somewhere between the two must approximate to a flat surface but I suspect it will be more S shaped on its side. Perhaps there is no total answer to the situation.

Harold

[Ramon WilsonParticipant @ramonwilson3]

Harold, Neil, Olaf,

If I may come back in here on this again – I believe this is one of those machining situations – using readily available conventional kit – that 'generates' a surface as opposed to the milling one would expect.

As referred to above I came across this very situation when milling the little end brasses on the Waller engine using a dividing head on the mill. I milled across the brass until the centre lines of the dividing head and mill conicided then rotated the the head 180 degrees moving off centre again to mill the opposing side. The resultant convex surface around the radius was unexpected and at first bemusing but it was obvious it was caused by the relief in the cutter. As said it proved much easier to take a pass straight across, moving the dividing head one turn each time to give a series of very small flats which were then quickly smoothed using a fine file.

These two pics showing the set up but are not particularly good – difficult to see the 'crowning' but give an idea. (The cutter has been moved up from the cutting position in the second image)

 

I don't see that offsetting the cutter will give a 'true' surface using any form of endmill/slot drill. Any style of such cutter formed with a flat bottom will by its very nature rub even though Neil has a point about the curvature. As I see it – to answer the original question – the only way to do this in one pass is to rotate the axis of the dividing head and use a side and face style cutter as previously suggested by 'Slot Driller'

Gosh look at the time – I'm missing my beauty sleep

Regards – Ramon

Edited By Ramon Wilson on 16/09/2012 00:03:07

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Michael Gilligan on 13/09/2012 17:09:32:

Michael Wiliams,

Many thanks for introducing the right terminology

I have been busy on Google, and just found this very useful eBook.

MichaelG.

Gentlemen,

Please have a look at Fig 2.2 in the link that I posted on Thursday.

I am sure that Michael Williams was correct; although the way to calculate the required desaxe offset currently eludes me … trial & error would get you there eventually; but it's nicer when the settings are predictable.

MichaelG.

[Harold Hall 1Participant @haroldhall1]

Before reading the latest posts, I was thinking of saying that I should have said earlier that a flat ended mill will not cut adequately for normal milling, then adding that for this reason such an end mill is very unlikely to exist commercially. Then leaving at that as there are errors in my other comments, for which I am sorry Olaf.

However, now viewing the latest by Ramon, a very interesting idea, and Michael Gilligan's reference to Michael Williams earlier post, I see that he was suggesting something that I commented on at the end of my last post. He, doing this, much clearer than I had done, and in fewer words. This being the effect of the degree of offset of the cutter above the workpiece's axis.

I am sorry Michael W for not reading your post but having been without access to the web for around a week due to a router failure I am struggling to catch up with emails, etc, received during that time. I think Olaf that the idea is very well worth trying.

Harold

[Harold Hall 1Participant @haroldhall1]

Sorry, post got duplicated for some reason

Harold

Edited By Harold Hall 1 on 16/09/2012 09:07:30

Edited By Harold Hall 1 on 16/09/2012 09:08:34

[Anonymous]

I agree with Ramon; I don't think it is possible to generate a true cylindrical surface using a cutter that has a concave underside.

It is possible to approximate the cylindrical surface by either of two methods, using a full width cutter. One,as described by Ramon, if the cutter is transversed across the work, with the work stationary, it will generate a plane surface. If the work is rotated slightly and the cutter traversed again it will generate another plane surface at an angle to the first. If enough planes are generated then they will approximate a cylindrical surface. Second, if a cut is made with the cutter fixed over the rotational axis of the work, and work rotated we end up with a surface that reflects the relief on the underside of the cutter; which prompted the post by the OP in the first place. If the cutter is now moved slightly to one side, and the work rotated again then the cutter will remove some of the 'hump' in the middle of the original cut, and so on.

And before anybody asks, I have looked at Fig.2.2 in the link above. I don't think that the figure is saying anything startling. It is simply stating that if you move a circle along an axis you get a cylinder. Likewise if you rotate a line around an axis you get a cylinder. Lastly if you rotate a curved line around an axis you get a concave or convex barrel shape. I don't think it is applicable to this discussion.

Regards,

Andrew

[blowlampParticipant @blowlamp]

You could always set it up in the lathe and use a Filing Rest

Martin.

[Michael GilliganParticipant @michaelgilligan61133]

Andrew,

I don't know if this helps but … any end-mill or slot-drill with a concave underside is, in extremis, effectively just a multi-tipped flycutter.

Your penultimate comment is therefore highly relevant; and a FLAT barrel shape is the special case that is exactly on the tipping point between concave and convex.

MichaelG.

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Clues :

With cutter on axis cutter looks concave to the work and a convex profile is generated .

With the cutter offset by its diameter or more the cutting edge looks convex to the work and a concave profile is generated .

[Anonymous]

If I understand correctly the premise is as follows:

1. With the cutter on axis above the work a convex profile is produced, as illustrated by the OP

2. With the cutter off axis by more than its diameter (and presumably offset in Z too) then a concave profile is produced

3. Between the convex profile (1) and the concave profile (2) there is a point where the cutter produces a profile that is neither convex nor concave, ie, it produces a cylinder

I agree with 1 and 2, but I do not see how 3 follows as a consequence. I do not think that 3 follows from 1 and 2 because the effects in 1 and 2 are produced in different ways. The convex profile in 1 is produced as a result of the clearance angle on the bottom of the cutter. If the cutter was flat across the bottom, as requested by the OP, then it would not produce a convex profile. The concave profile in 2 is produced by the intersection of the circular cutter and the rotating work. It makes no difference if the bottom of the cutter is flat or concave.

There is a point at which the cutter will produce a profile that is neither convex nor concave, but it is when the cutter is offset such that it touches the work at a single point, and therefore isn't really cutting.

Regards,

Andrew

[JasonBModerator @jasonb]

The only problem with all this off setting is that you also start to alter the overall width of the cut and also loose the straight sides. So to avoid this happening you would need to take take additional cuts to square up the sides to the required width in which case you may as well take several passes with a smaller dia cutter.

The other option is to just take a file to the convex bottob that the OP has now and file it flat

J

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 17/09/2012 14:55:25:

The other option is to just take a file to the convex bottob that the OP has now and file it flat

J

Thats definitely the expedient solution for a one-off, Jason.

MichaelG.

[ChrisLHParticipant @chrislh]

Just to do it to death how about :-

Mill slot using standard end mill thus leaving a convex surface

Set up in the lathe and then rotate the work back and forth by hand through part of a revolution to trim off the excess using lathe tool, cross slide, etc. as in normal work. As we are talking small nimbers of thous. this should not take long.

[Author]

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