XL pulley 4 axis cutting

[ArtF]

Ozzie:

You can slow the animation to as slow as you wish with the slider, the root cuts just make the sides flat is all, the tangental will try only to shave the upper radius, its the only curve it sees. But if you turn on the simulation and slide the slider down to slow you should see the motion better.

Art

[ozzie34231]

That's not correct Art. I am watching it with the slider all the way down.
Anyway, with the sim zoomed in so it just envelops the action, and tilted for the best observation I have watched what is happening; watched it for quite a while, and I don't see the walls of the pulley being cut.
During "tangential" the tool only shaves the small radius, goes down outside the pulley and loops over to the opposite radius to shave that.
During "rooting" the tool only goes straight down, no movement of the 4th axis except to move to the next tooth.
What am I missing?

[ozzie34231]

Here's another shot with the color changed slightly. Only the bright green are cuts.

[ArtF]

Ozzie:

  Doesnt sound liek your missing anything. The root wall routine rotates the blank so the root wall thats straight is cut in a single pass, the tangental wont try to cut anything that isnt curved, curves are the only thing tangental can really do. As the root wall is a straight line vector, the program puts a single line pass on it to straighten it, then applies the tangental only to the radius at the top. Unlike normal spurs, the side walls of that
timing pulley have no real curvature. The bottom radius cannot be cut by either so
the rooting section does the best it can there.
  So in your case it sounds like the rootiing isnt doing what it should, but it may be trying to do it in one pass, in which case the smallest radius at the bottom is all thats cut. If it is rooting in passes, each higher pass can typically cut a bit wider.  Change your depth per pass and see if the rooting ( not the root wall) cuts wider on each pass..

Art

[ozzie34231]

Okay, I see.
With a flat mill you get a stepped wall.
I might try making one with this method but I think I'll go back to making a full profile cutter, similar to a gear cutter.
Many thanks though, very cool program Art.
Jerry "Ozzie" Pryor

[ArtF]

Ozzie:

Yes, with a pulley you end up with a stepped  radius at the bottom of the tooth,
the walls should be straightened with the wall routine though. A radius bit tends to
make it all come out ok as that bottom radius is for relief and the belt doesn't usually run into it.  Doing it with a shaped bit is always preferable for a pulley though, there
just isnt enough curve in there to shave.

Art

[ozzie34231]

Hi Art,
Steps at the bottom radii don't matter, and at the top the shaving should be fine.
But I don't understand your statement regarding the walls being straightened by the wall routine, I take that to mean flattened. The only way I get any taper on the walls at all is to make small depth increments as you suggested. That makes steps in the wall the size of the depth increment, certainly not flat.
It seems to me that while not the same as making a gear tooth, it should be possible to shave/cut the side wall with the 4th axis rotated and the tool offset the proper amount.
The wall routine does not do that.
Ozzie

[ArtF]

Ozzie:

I agree, purely a problem due to the fact the routine is meant to do gears as opposed to pulleys. Its a problem where shaving is done on the curve, and with no curve the algorithm is a bit lost as to how to do the wall. Ill add this to my list of things to look at in gearotic, it is definitely a deficit. Works well as designed, but pulleys are kinda a get what you get type of operation , though to its credit Ive seen many done that worked very
well and the user was quite happy. In this case the XL's wall is at the bad end, the GT's seem to have far less trouble. Your shaped bit idea is probably the best way to go, and it is the way I always recommend for pulleys if you have the technology to make one.

Art

[ozzie34231]

Cool.

Your avatar reminds me of the early days of Mach 3 Turn. A few of us were wanting threading, but A. F. kept producing improvements and features until someone said "you don't have a Turn program until it threads". It must have been the right 2X4; we got threading.
Cheers,
Ozzie

[Campgems]

I seem to be jumping into this boat a long time after it left the dock, but here goes

I'm trying to lay out a set of 3 XL pulleys for the motor to spindle on my Taig Lathe.  My choice was 18T, 36T, and 54T stack for 1 to 3, 1 to1, and 3 to1 ratio.  I keep getting the notice that my mill is to big, event though I've gone down to a 0.020" with a 0.005" radius on the corners.  I can easily set a 1/16" square bottom mill in the bottom of an 18 t Commercial pulley without fouling the curve at the bottom.  What I'm I overlooking here?

Don

[ArtF]

Don:

  Ignore tool warnings in pulleys. The 4th axis was designed for tangental cutting, it relies
on the fact that an involute curve is continous on its tangental relationship to the vertical
tool over its curve length with rotation.  This is a fancy way of saying as the gear turns,
the next tangental relationship is slightly ahead of the previous.
  Pulleys arent so. They follow no math and are in many cases made of arbitrary curves
concatenated to each other by specification. There is no way to ensure a tangental cut
will work, BUT they most often do. Use any tool you figure will work by watching it in
simulation, if it looks like it will work, it likely will. Pulleys though can leave some area's
not cut, luckily belts tend to allow a lot of variance.

  Best 4th axis pulleys are done with a shaped cutter as in Gearotics output, BUT Ive cut a few
and seen quite a few samples from users that show the tangental routines can cut them
quite efficiently in many cases. Another way to get them perfect is to cut them in 2d
where the full shape can be followed correctly.

  But generally, ignore tool size warnings in 4th axis with pulleys, the tool size calc is done
with involutes in mind.

Art

[Campgems]

I'm having a similar problem, but it is enough different that I don't think it is the problem described above, and maybe it's my misunderstanding of the tool description

The issue is this. The pulley is an XL pulley.  All research on that form shows the bottom of the pulley grove is 1.27mm or 0.050"  The radius of the bottom and top curves is 0.61mm or 0.0025"  I figured a 0.005 radius mill ( the finest radius  I found ) would leave a slight amount in the bottom that the belt wouldn't tough.  So I defined the tool in the tool table as a 0.050" flat mill with a radius of 0.005" and bottom flat of 0.040"  The profile of the mill in the simulation looked good, but the mill cut beyond the diagonal 25 degree slop of the sides and it also posted a warning the mill was too big.

I make it a sharp corner 0.050" mill with no radius, there is no fouling of the slope sides in the simulation.
If I make it a 0.030" with the 0.005" radius it is OK also.  But a mill over O.034" fouls the side.  My guess is that either I don't understand the tip radius and it really doesn't apply for this application, or that the radius isn't calculated in the edge of the tool.

A kick in the right directions would be welcome. 

Don


What am I missing?  I'm new to the program, so

[ArtF]

Hi Don:

  The end radius wont be taken into account. In tangental shaving the radius at the
end is not material to the algorithm. The algorithm tries to align tangental points on a curve
to the vertical axis of the tool ( so only the edges). This works well in involutes. While never
planned for pulleys it turns out they do often work as well, but its hit or miss until it simulates well.
It really depends on the pulley type. If the root walls are a tangent to the center it tends to work
ok, but in some shapes it simply gets as close as it can.

  The algorithm in 4th axis is actually just trying to figure out how best to place the tool
at various steps along the way without hitting the stl 3d model of the tooth.

  Thats not to say a radius on a tool wont matter, even in involute cutting it still will make the
root more rounded in its trochoidal root area. But all cutting will really be attempted
at the bottom edge of the tool  on each step,unless "Maintain depth" is checked, in that case all cutting
will be attempted on the side edge of the tool so the tool will be kept lower.

  With pulleys I usually advise using a shaped cutter to the dxf shape if its a small
pulley, or failing that to try to make your settings so a slow run in the sim looks safe
and as close to pulley tooth shape as you can get. The warnings wont mean much
in many pulley types.

Art

[Campgems]

Thanks for the reply Art.  I figured the bottom radius of the XL pulley isn't an issue as the belt will not get that low anyway, but the upper side to OD radius may be. I'm guessing that as the radius is only 0.024" , a couple licks on the sharp edge with a file would probably be good enough.

An involute type cutting wheel would be best, so I might just opt for that route.  Home made though.

Thanks again for the help and explanation.

Don

[ArtF]

Anytime,

  Luckily for me my pulleys are such that I can 3d print them. They can be a bit of a bitch
in 4th axis.

Art