Endmill, Slot Drill

Edited By Terryd on 01/12/2010 10:55:35

Secondly the advancing flutes will be cutting in conventional milling mode while the trailing flutes will effectively be cutting in climb milling mode. The load on the advancing flute, in normal mode, is significantly higher as it is trying to penetrate the surface at an acute angle while the other flutes and portions thereof are cutting at their designed optimum with much less side load .

Its a wonder that a mill cuts straight at all . Don't think I want to ponder it too much but it will give me a scapegoat when I make a pig's ear of a job.

Edited By Martin W on 01/12/2010 19:38:05

Hi All,

I have a question. The crosshead shown in the photo is made from cast bronze. It is complete except for the slot which needs to be cut for the small end of the crankshaft. The size of the slot is shown in the drawing 5/16" wide and 1/2" long. My question is what type of cutter is best for this job? I will be holding the work, using a vertical slide and vice using the small fixture (or is it a jig?) to set the gudgeon pin hole vertical.

My thoughts are that as this is a "closed" slot a two flute cutter may not be the most appropriate choice. What do you guys think?

cheers geoff

Hi All

doh!!!!!!!!!! connecting rod not crankshaft.

Two or three flute every time if the slot width is critical.

Russell

Hmm. 2 and 3 flute cutters are less rigid due to the smaller remaining "core". And there can only be a fraction of a flute in contact (and cutting) with the work at any one time, especially with the light cuts we tend to see in this context (hobby machinery etc), so the cutting will be very much intermittent which isn't good for surface finish or dimensional accuracy. They are generally recommended for heavy roughing, as the large flutes are good for chip evacuation.

On the other hand, multi flute cutters have a more rigid core and are more likely to have one or more flutes in continuous contact with the work. It's probably not a great surprise to see that these are recommended for finishing. Even better when combined with odd number of flutes and variable pitch flutes that minimise resonance vibrations. If you had a big chequebook you could buy a groovy finishing cutter just for the job with a high flute count.

I suspect there won't be a massive difference between 2, 3 and 4 flute in this instance. It's more likely that the accuracy will be determined by setup, human error, backlash etc.

Murray

The only way you could do it with a conventional 4-flute endmill - which don't generally (or maybe ever?) endcut to centre - is to do the 2BA hole through first, then feed the endmill down it prior to opening the slot sideways in both directions.

There'll be an assymetric tendency to form oversize radii at both ends with the 'lobes' in opposite directions, and the whole idea assumes that the noncutting counterbore in the end of the mill is smaller than 2BA tapping size - and you'd have to be a bit cute about getting it right.

Easier to use a vanilla 5/16" slotdrill, or maybe 8mm to get yourself a couple of thou play.

I do the same sort of cut for the inside of IC engine pistons.

Drill to depth with a drill one size smaller than the 5/16. Change to a 2,4 or 4-flute cutter and plunge to depth, move say 10thou to the side and plunge again. Do this until you have one side to finished length then repeat for the other and then finally move the work the full length of the cut to clean the sides.

Hi All,

Thank you all for your responses,

I've done it now, 2 flute, nice and steady 5 thou max cut, clean as whistle.

My original post was perhaps misleading. My concern was not so much accuracy but more the way a 2 flute cutter would react. You could just feel it clipping the gudgeon pin hole but otherwise no problem.

The more I get involved with model engineering the more I enjoy it but there are times when using machinery and you are stepping into the unknown, well it can a little nerve wracking!!!

thanks again geoff

No-one said it was easy but, SOMEONE HAS TO DO IT !!