cam groove

[chrisb]

Thanks for the explanation. To make things a bit clearer I have replaced the image above, now it shows the section.

You are right, the normal of the path is tilted by 30° and that's the difference to a helix.

[emills2]

right, a typical helix will always have a flat frenet. a typical helix will also be perfectly related to the cylinder in which a thread is being cut, because the cylinder and helix will have exactly the same main axis.

[chrisb]

If it comes to machining: have a look at sliptonics video:

phpBB [video]

[NormandC]

emills2, your posts have been very informative. Thank you!

Personally I don't mind closed-source CAD programs being mentioned here. In fact, over the years I've redirected newcomers to those solutions when it was clear that FreeCAD couldn't do what they needed.

Of course I'm glad to know that in this case you found FreeCAD was better than Onshape

[TheMarkster]

If at third you don't succeed...

This time I incorporated the source from the 3d parametric macro into this macro, so no need to install and rename that macro. I made a couple minor changes to the source after incorporating it, one to remove a bug that was causing an exception, the other to comment out the code to show that gui.

I uploaded the model created with the macro, but had to remove some of the objects that were used during the process, namely the bsplines and the ruled surfaces. If you run the macro you get all the stuff I deleted to make the file small enough for the forum.

Strategy this time is to make the original bspline as before, we make 2 the same size using the 3d parametric curve software to do it, as before, only this time instead of using it to make 2 new bsplines with the different radius for the slot, we use draft scale operation, scaling x and y, but not z. I think (maybe) all of the cut slots are now perpendicular to the cylinder axis (but I thought the same thing before and was wrong.)

There are 4 bsplines, call them minor1, minor2, major1, and major2, with minor1 and minor2 having the minor radius of the inside of the slot to be cut, and major1 and major2 having the radius of the cylinder. minor1 and major1 remain at the same z position as when created, but minor2 and major2 get moved up in the z direction by the amount of the slotHeight parameter. The difference in the radii is the (slot) depth parameter. With the 4 bsplines positioned as such, 4 ruled surfaces are created to connect them into the box shape, the shape into a shell, the shell into a solid, the solid cut from the cylinder.

I've also worked out that using strokeFactor = 1 produces a total stroke length equal to the radius of the cylinder. So if the cylinder radius is 50 and you need a stroke length of 25, then use strokeFactor = 0.5, for example.

I made the slot object manually using dwires instead of bsplines so I'd have some lines with which to use the measuring tool to check the angles. All of them came up 90 degrees that I checked.

yac(v2)dwires.gif (839.38 KiB) Viewed 1113 times

[oldmachine]

it can be done more easily with PartDesign - but, you know that... (and, can use bspline or simple radius')

[TheMarkster]

New feature: select how many strokes per revolution (by editing the source).

Code: Select all

radius=60 # radius of cylinder
depth=5 #depth of cut (along x/y axis)
slotHeight = 5 #height of slot (along z-axis)
innerRadius = radius-depth
strokeFactor = 1 #length of stroke along axial direction (1 = radius, 2 = 2 * radius, .5 = .5 * radius, etc.)
cylinderHeight = 100 #length of cylinder
strokesPerRevolution = 2 #should be an integer 

Here's one with 12 strokes per revolution:

yac3.png (98.94 KiB) Viewed 1098 times

(But I did run into some self-intersection issues with values greater than 4. Still not sure if this produces a valid cam path, but I figured since it was easy enough to add this feature...)

[chrisb]

Hi Oldmachine, I would prefer to see the FreeCAD files rather than the images. The latter can be easily derived from the former but not vice versa. Images tend to fool the eye.

[oldmachine]

I don't mean to appear rude by saying:

Speaking of “…rather…”, I would rather those who comment on my approach(s) to actually try as I suggest before complaining…

With respect to this Cam Groove thing: I clearly stated it’s a concept and the curves can be tweaked to (users) liking.
Nobody that complained (including yourself) appears to have tried to tweak the groove (such as to widen it where you pointed to it being narrow). It took me about 20 seconds to do it. And, 'NO' I did not tweak it to what I would do for a real part - only to show the simplicity of doing it...
I knew it was narrow but left it to others to play around with.

As far as the surface in the inner area of the groove, I don’t care about that - there were no spec’s/rqmt’s provided and the cam follower will rest on the side walls.
The cam-follower’s arm can be spring loaded to keep it in contact so, a groove isn’t even necessary.

At the inner boundary where someone pointed to a millimeter of sloped surface, a cam-follower with a radius’d tip would be happy. But, the depth of the groove could be deep and the follower pin/bearing can be short (options… it’s not an iPhone). ‘My only’ interest is the guiding surface. And, if only for a Fluid/Air-Pump or non-precision gizmo, a FreeCad Show&Tell etc, positional accuracy is irrelevant.

So, posting files appears to be only a vehicle for others to find fault with and I won’t bother posting them. You’re all smart and experienced with FreeCad enough to glean how I did it from the items shown in the Tree.

I printed several cam parts and after I fix my Harley over the next few days, I'll (maybe) post a photo...

Those cute animations and sketches are pictures, not real parts.

[chrisb]

Speaking of “…rather…”, I would rather those who comment on my approach(s) to actually try as I suggest before complaining…

With respect to this Cam Groove thing: I clearly stated it’s a concept and the curves can be tweaked to (users) liking.
Nobody that complained (including yourself) appears to have tried to tweak the groove (such as to widen it where you pointed to it being narrow).

Well, I have played around with your proposal and I have uploaded my findings here; so I don't quite understand where from you get this impression.

I have uploaded myself numerous models to this forum as proposals which turned out to have flaws, but in the end the result was better than any of the initial uploads of any of the participating members.

This is the point where I am out of the discussion.