CNC Crankshaft Machining

[Vixen]

Hello Kvom

Did you notice the original JS code  for O003 and O004 (when simplified ) was as follows

Z + [ bar rad minus pcd rad plus pin rad * passes/count}

whereas your code appear so have

Z + [ bar rad minus pcd rad minus pin rad * passes/count}

With the plus, the overall depth of cut becomes 12.5 mm not 2.5mm

Hope this helps

Mike

[Jasonb]

Stuarts latest screen shots would also work assuming the wide gap between the circles on the left is 1mm and diminishes to about 0.06mm on the right.

This would give a full 1mm depth cut on the wide side of the crank reducing to a very shallow depth on the side nearest the pin. What we don't know is when John said "1mm per pass" is whether that was a maximum or a fixed depth. Fixed depth would be better as you would almost be rubbing the corner off as the DOC got to the shallowest part.

[kvom]

I reworked the linux program so that now rather than specifying the number of passes you specify the maximum depth of cut, and the number of passes is calculated.  This max DOC is attained only at the 180 degree point, and is pro-rated around the bar based on the position of the top of the pin.  The attached photo of the PP screen shows the paths for each of the passes.  These are not circular.  I believe the program is quite easy to read and understand at this point.

Note that since all the A/Y/Z moves are coordinated, the actual cutting feedrate is quite small, so an appropriate doc can be larger than you might think.  My A axis appears to turn at 300 degrees/minute.  At this rate the SFM of a 2" diameter bar is ~5.2 ipm.

[Stuart]

Nice work there KVOM

It took me a while visualise the paths required

Looks like your version is a better way to use for different jobs

The JS one seems to be critical in the setup

May I try to port your version over to a Mach/fanuc version


Stuart

[Vixen]

You have been busy Kvom.

I downloaded your latest version into  LinuxCNC ver 2.7

The toolpath plot  showed an elliptical tool path opening to a full circle with each successive pass. We have seen a similar elliptical plot way back in your Reply #22 post. I will go back and revisit this version later.



I entered the standard 30 bar 15 pcd 10 pin parameters (converted to inches) and a 1 mm (0.04" pass depth.

This is a photo of what was produced. The pin, coloured black, is crescent shaped, the "machined" toolpath was a double loop. The narrow dimension of the crescent is 10mm



The most significant thing I noticed was the Y axis was moving to the opposite end rather than staying vertically above the pin. The Y axis is moving in ANTI PHASE to the pin

Can we assume a numerical Y axis sign change would sort this

Alternatively reversing the direction of rotation of the 4 th axis would sort it

Or by turning the 4th axis around through 180 degrees. I think Jason mentioned something about JS having his rotary on the right.

I will play around a bit more

Regards

Mike

[Vixen]

BINGO It works.

What a difference it makes, just reversing the effective direction of rotation of the A axis.

I did this, by turning the 4 th axis head through 180 degrees on the table. The Y axis movement is now IN PHASE with the movement of the pin and always remains vertically above it.  The "machined" tool path now produces a perfect circular pin of 10 mm diameter.

Compare this circular pin with the one in the previous post. The program is the same, only the direction of rotation of the A axis has changed.



Kvom, is it possible to offer the option of incrementing or decrementing the rotation count to offer two directions of rotation to match the users set-up?

This has been a long hard struggle by Kvom. Well done that man. It is not easy to visualise all three axes moving together particularly movements relative to a rotating axis.

Regards and Respect

Mike

[Jasonb]

That looks like it.

Mike, bit hard to tell from your tool marks but did the cutter start buy cutting a full circle be it of varying DOC or did it do increasing length arcs until the last few rotations here the tool is within the 2.5mm of the narrow side?

Now if only you would stop playing with those radials and make something that needs a long crankshaft

[Vixen]

Now if only you would stop playing with those radials and make something that needs a long crankshaft

Oh! do you mean something like a Mercedes Benz W165 crankshaft or a Porsche 917 crankshaft? Why did you think I was paying so much attention

In answer to your question. The narrow side has 2.5 mm removed and the wide side of the bar has 17.5 mm removed. The depth of cut is 2.5 / 18 at the narrow side and 17.5 /18 at the far side. The "machined" tool path (that's a new definition for the dictionary) describes a nearly circular orbit removing more material from the 17.5 side.

We have very little control of the actual feed rate, it is effectively controlled by the cycle time of the subroutine loops. The amount of material removed is much greater for the early cuts and reduces as the final small pin diameter is reached. A final spring cut at the final diameter would be nice.

The cutter is effectively 'conventional' milling on the right hand side and would be 'climb' milling on the opposite side of a slot. I had used up all my long series, end cutting mills during these experiments. I only had this one last, worn out, cutter left to play with, thence the poor surface finish.

Happy happy

Mike

[kvom]

The Y direction issue seems obvious once you see it.  The easiest "fix" is just to reverse the sign of Y in line 30. 

Change Y[#<Y>] to Y-[#<Y>]

[Vixen]

The Y direction issue seems obvious once you see it.  The easiest "fix" is just to reverse the sign of Y in line 30.

Hello Kvom

It is only obvious when you see it being machined, who would have guessed, if you only look at the YZ plot on the screen.

Two small points. A additional spring pass at the final pin diameter would be nice as would lifting the cutter clear at the end.

That is a brilliant piece of work from you. I admire your persistence. It is doubly difficult and frustrating when you cannot visualise the final "machined " tool path

Mike

[Vixen]

The Y direction issue seems obvious once you see it.  The easiest "fix" is just to reverse the sign of Y in line 30.

Hello again Kvom.     Which is line 30?  Is it the G01 F A Y Z line at the bottom of O004 sub?

Mike

[kvom]

Yes.  Change Y[#<Y>] to Y-[#<Y>]

A parameter at the top (1 or -1) could work, but it would need to be documented in comments based on whether the top of the rotab move away or towards you.

Lifting the tool at the end would be a final line in the main:  G0 Y[#<_bar_radius>]

Spring pass would just be:

#<_passcounter> = #<_passes>
O003 call

After the O103 endrepeat line

[Vixen]

Yes.  Change Y[#<Y>] to Y-[#<Y>]

A parameter at the top (1 or -1) could work, but it would need to be documented in comments based on whether the top of the rotab move away or towards you.

Thanks Kvom. If you edit your reply #77 with the above information, that should be enough.

Mike

[Vixen]

Me again Kvom,

I think that if you were to reinstate all the sin and cos functions back into the two subroutines; then you can use variable #5 <angle> as the pin position angle ie. 90 degrees, 180 degrees, 270 degrees or whatever.

That said, it may be safer to set and re-zero the pin angle and the x axis offset manually, at the start of machining each throw.

Mike

[Vixen]

Yes.  Change Y[#<Y>] to Y-[#<Y>]

Na, Changing Y[#<Y>] to Y-[#<Y>] did not do it. The A axis still turns the same way with either.

Just found the new edits in Reply 86.      Thanks

Mike