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CNC'd Loco Wheel & Earning Brownie Points
philf:
John S very kindly send me a Cut3d generated file which I have just tried to machine.
The wheel should have been finished in 2 raster passes at 90 degrees to each other.
Unfortunately, 3/4 of the way through the first finishing cut, my Z axis lost about 5mm worth of steps and I couldn't rescue the part. :(
My machine still has an acme leadscrew on the z axis and can't run very fast without stalling. I have a ballscrew to fit but the machine will need a lot of modification to accomodate it. A gas strut might help to take a lot of the weight of the knee.
The first picture shows how it cut and how the fillets on the spokes look. They look very good and don't show the problem that the Aspire wheel showed! (Strange that Cut3d and Aspire are both from Vectric!)
The next picture shows the steps which are produced by rastering. The second finish cut (at 90 degrees to the first) would have cleaned these up.
John estimated 51 minutes - Mach3 told me 1hr 14minutes which is probably down to my slow z axis.
There is one feature in MeshCAM which ensured a good finish to the rim and the inside of the spokes - it has a 'waterline' finishing feature which runs round following the profiles in steps . It also has raster finishing in either one or two passes.
I don't know why MeshCAM needs to do the inside of the spokes in many passes as the sides are vertical and would machine just the same in one pass. I've asked the question of the software developer as I may be missing something in the settings.
I'm doing no more in the workshop today.
Phil.
fatal-exception:
The raster looks good for an ACME z-screw. The Waterline finishing would improve the overall finish. \
If I were to do that part, I would probably start by pocketing everything that can be pocketed. Raster with a ballnose in probably a couple of directions, then do the final finish with the waterline type of program. If you want an extremely fine finish, decrease your stepover and ramp up your feeds, and use the largest tool possible.
Anyways, looks good! It's always fun to finish 3d parts! :clap:
Paul
philf:
--- Quote from: fatal-exception on May 07, 2012, 05:12:53 PM ---The raster looks good for an ACME z-screw. The Waterline finishing would improve the overall finish. \
If I were to do that part, I would probably start by pocketing everything that can be pocketed. Raster with a ballnose in probably a couple of directions, then do the final finish with the waterline type of program. If you want an extremely fine finish, decrease your stepover and ramp up your feeds, and use the largest tool possible.
Anyways, looks good! It's always fun to finish 3d parts! :clap:
Paul
--- End quote ---
Hi Paul,
Did you see the photo of the wheel I did with code generated by MeshCam? It did include waterline and pencil finishing - if it had been in metal, the rim would have been good enough to run on.
The rads on the ends of the spoke are 2mm and that's why I used a 3.5 mm b/e cutter with a 0.35mm stepover.
I have looked at some old loco wheels and think that I could get away with having rectangular section spokes without the corner radii. I could then machine a blank in 3d and cut out the spokes in 2.5d. MeshCam doesn't have any facility for 2.5d machining so I'd have to use Cut2d as well.
The ACME screw will have to go but it can wait until I'm in the mood for stripping the machine down. (I have a job for the Acme screw on a diy surface grinder project). I acquired a freebie 2505 ballscrew to fit but it has a double nut which is 150mm long - I don't want to lose that much travel and so I am thinking of using just one of the nuts. I'm not sure how much backlash there'd be. There is another option and that would be to use one nut above the mount and one below. I'd have to raise the base of the mill because the screw would try to bury itself in the concrete floor!
Cheers.
Phil.
fatal-exception:
Yeah, that wheel looks great!
I've never really used MeshCAM, probably had a look at it at one time, but I settled on ArtCAM Pro, which seems to do a nice job of any 3d I throw at it. I use SheetCAM for all the 2.5D stuff, been using it for years and it's never failed me.
I know about the ball screw retrofitting. Making sure everything will align and fit takes considerable time. I have a largish mill that is next on the list for ball screw CNC conversion. (ZAY7045) Not really looking forward to the project, more towards the finished product.
When I designed my router, I used double nuts on each axis. That was about 5 years ago, and there is still no noticeable backlash, and I've only adjusted them once. I guess it all depends on how accurate you need to be. Try to use both if possible. It sounds like you will be driving the nut(s)?
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