milling crankshaft on cnc mill using A axis

[geoff adamsParticipant @geoffadams14047]

[geoff adamsParticipant @geoffadams14047]

iam working a midget engine and wanted to rough out the journal on the cnc mill i wrote a program but Jason B sent me link for program all i had to do was enter the stock dia the throw of the journal and dia of journal

if anyone is interested in the program iam sure Jason will post the link

iam very impressed very easy to set up

Geoff

[JasonBModerator @jasonb]

That is better than the usual thump, thump, thump of turning from the solid. I wonder if a flat ended ctr cutting bit would work better than the rounded one you were using as the cutting speed at the edge of the tool should be faster.

For those interested the program is one the late John S wrote and used to demo the Sieg CNC machines at shows. Works straight out of the box for machines like the Sieg that have their 4th axis on the right but needs a slight tweak if it is on the left.

[nigel jones 5Participant @nigeljones5]

that would make life simple…if only I ever dared to fit my 4th axis. Why not go the whole way and cut to size with a flat tool? Surely a good finish is possible? My cnc computer got filled with dust and went pop earlier in the week so had to drill 300 holes by hand, awful job! Time to build a decent enclosure for the pc and driver box so it doesnt happen again. Theyre great when they work!

[geoff adamsParticipant @geoffadams14047]

the cutter is an 8mm flat slot drill i think its the video gives the impression its a rad cutter

Geoff

[EmgeeParticipant @emgee]

Jason

Is the crankshaft program available from your Dropbox with a link please ?

Emgee

[JasonBModerator @jasonb]

Can be copied from the first post in this thread, also a Linux version further on, JS's was for Mach3

[Martin ConnellyParticipant @martinconnelly55370]

F50

G19

G01 X0 Y0 Z10 A0

G060 A360 Y0 Z10 K10

G17

M30

Try this. Gives the required motion. Simple to understand. I could add parameters to allow for throw and pin radius and offset for subsequent pins. This will currently give a zero diameter pin with stroke of 20 if the bottom of the cutter is on the a axis centre line when z=0. Bottom of the cutter 3mm above a axis centre line at z=0 gives a 6mm diameter pin.

Martin C

 

 

Edited By Martin Connelly on 02/02/2020 18:34:52

[Anonymous]

Posted by fizzy on 02/02/2020 17:28:52:

Why not go the whole way and cut to size with a flat tool? Surely a good finish is possible?

Standard endmills and slotdrills are not flat on the end. They're slightly hollow ground, so you end up with a barrel shaped crankpin not a cylindrical one. The problem can be ameliorated, but not eliminated, by offsetting the cutter.

Andrew

[Martin ConnellyParticipant @martinconnelly55370]

F50

G19

G01 X0 Y0 Z10 A0

G02 A360 Y0 Z10 K10

G17

M30

Fixed the G02 line. Didn't see the corruption caused by editing the line.

Martin C

[Martin ConnellyParticipant @martinconnelly55370]

F50

G19

G01 X0 Y0 Z10 A0

G02 A360 Y0 Z10 K-10

G17

M30

Added the minus sign in K-10

This is what happens when you type it in here before checking it in Mach3.

Martin C

Another thought, G02 may need to be G03 depending on the a axis positive direction.

Edited By Martin Connelly on 02/02/2020 20:06:26

[Ian Johnson 1Participant @ianjohnson1]

Great to see some 4th axis CNC and using a John Stevenson program too! Turned out nice.

I use Vectric Vcarve which uses the Z axis as the A axis when rotary milling, bit of a cheat really because it is still only three axis milling not 4 axis. So I had to start writing my own programs for true 4 axis milling, nothing as ambitious as this though!

I need to get my 4th axis plugged in, not used it for a while, I also need a tail stock support like yours before attempting something like a crank.

Is it an optical illusion or is the cutter slightly off centre to the journal?

Ian

[old martParticipant @oldmart]

I take it that the finishing cuts after the photographs were taken were by resetting the Y axis two or three times to get the journals cylindrical.

[EmgeeParticipant @emgee]

Jason.

Having read all posts on the MEM forum am I correct in thinking the first Mach3 posted code is functioning correctly provided direction of the A axis is correct ?

Emgee

[JasonBModerator @jasonb]

Emgee, Yes, that is the one Geoff used.

Old Mart, no the middle of the pin is slightly raised due to the shape of the end teeth of a typical cutter as already mentioned by Andrew as the cutter always stays directly above the pin's ctr line by moving in the Y axis.

Should also say that it was mostly written by Adam, John's son.

[old martParticipant @oldmart]

No, Jason, if the cutter stayed above the pin centre line the centre of the pin would be larger. Clearly the cutter centreline was offset as the machining marks confirm, making the pin smaller in the centre.

[JasonBModerator @jasonb]

I agree that the one Geoff has shown does appear to have fillets in the internal corners which suggests something is off, which is why I thought a ball nose cutter was being used.

This is how one done by JS looks with no additional passes after running the code.

Originally posted by JS in this thread with sketches by Andrew of how Y follows the pin

[old martParticipant @oldmart]

Is that a 7 cylinder engine with only 2 main bearings or what is it?

[JasonBModerator @jasonb]

Read the thread.

[old martParticipant @oldmart]

Found it eventually after the usual ramblings, just a demo.

[geoff adamsParticipant @geoffadams14047]

Morning all from the replies it seems that i have the y axis off creating a fillet in the corner

the a axis is left on the mill all the time i will check the set up this morning. mach 3 does lose it self, i relied on it remembering the y offset

anyway off to specsaves this morning to pick up new glasses that might help will let you all know how i get after resetting and checking the setup and running another test piece

thanks Geoff

[geoff adamsParticipant @geoffadams14047]

checked all settings bit of a blonde moment when setting the y axis used edge finder as 4 mm dia should be 5 mm so .5 mm off center now no fillets but it looks to me that the journal has a slight rad ?? any help please

Geoff

[BazParticipant @baz89810]

Hi Geoff, crankpin will be barrel shaped due to your milling cutter being hollow ground by a couple of degrees, you could grind milling cutter truly flat across the bottom or I think you can do another pass around the journals but with Y axis offset by just under half the cutter diameter, this should just flatten off the high spots.

[old martParticipant @oldmart]

Now you are seeing the cone shape because the end cutting mill leaves a surface higher in the centre. You could get the journal truely cylindrical with an infinite number of passes, each offset by an infinitely small ammount. You will only get the journals parallel if the tool has a flat end. The end product is a roughed out crankshaft ready to be finished turned , or ground.

[Anonymous]

Even with a flat bottomed cutter you don't get an exactly cylindrical pin. Assuming a finite number of flutes on the cutter you end up with a series of facets that are on a helix. On a practical note the centre of the cutter will be operating at a very small surface speed, so it is likely that the surface finish will vary across the pin.

Andrew

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