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I'm having trouble machining the radius of a fretboard. I made a new fixture out of double 3/4" HDPE for a tapered FB. I milled my spoilboard to get a new clean surface and checking with a level in all directions it looks balls on. However when machining with a 1" round nose carbide bit the FB is thicker along the Y1 axis than the Y2 axis by some .040 I am running the bit lengthwise parallel to the Y axis with a .020 stepover. I have checked and rechecked all my drawing dimensions and every one is on the money. Looking at the radius from 1 end it looks like the radius has just started the decline about 1/8" from the Y2 edge. Looks like the FB is too low in the fixture on that side. I know that HDPE cups along the length that's why I doubled it and screwed it down to the SP. Is it possible that the HDPE could vary that much. The fixture is 6" x 30" with a recess to hold the FB The recess is dead center in the fixture. I have a laser beam with a 1/2 shank that chucks into a tool holder and it also shows the FB dead center of the fixture. One more thing... I did not mill the surfaces of the HDPE. I just assumed it would be flat. Any suggestions. I'm using Rhino 5.0 & Madcam/ WinCNC processor.

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The Zootman
1109 Military Rd.
Kenmore, NY 14217
(716) 874-1498

Face your fixture flat with a .5 EM or larger, just as you've probably done with your whole spoilboard surface. It may be relatively flat out of the box but not consistent in thickness. You can try just skimming .010 off and if you have to, reset your Z=0 and run that again until the tool has touched the entire surface. I would not use a light duty spoilboard cutter on the plastic.

Use a dial indicator gauge to check things like the flatness of the fixture surface by slowly jogging over it. I have one that mounts in a spindle collet that I use for alignment checks, and also one mounted to a bar that I can swing down for quick checks of stuff like this. In the future you can quickly check to see if the fixture needs to be faced again.

Thanks Rand I'll give that a try. I have a 1 1/2" carbide cutter for surfacing the spoil board. I think I'll have to re-cut the FB recess too?

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Beautiful and unusual tone woods at a reasonable price.
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The Zootman
1109 Military Rd.
Kenmore, NY 14217
(716) 874-1498

Sounds like your fixture might be out of alignment with your toolpath by 1/8" or so.

Sheldon I lined up my Laser cross hairs on the left hand corner of the fixture and then ran the head down the Y axis to the far end of the fixture to align it. It seems to be right on. I have 4 fixtures that all mount in the exact same position . Where would be the best place to set X0-Y0 at the lower left corner of the fixture which should always be the same or at the lower left corner of the part which I would have to reset every time I change fixtures. I work with Z-0 off the top of the spoil board.

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Beautiful and unusual tone woods at a reasonable price.
http://www.rctonewoods.com/RCT_Store
The Zootman
1109 Military Rd.
Kenmore, NY 14217
(716) 874-1498

Bob,

When I read your post, my first thought was out of alignment like Sheldon mentioned. .040" would be a lot of out of tolerance for an extruded product, which I am pretty sure the HDPE is.

Bob you mentioned aligning everything off the edge of the fb fixture. Have you checked and rechecked your model in Rhino?

Did you build your model on a centerline, or even a half at a time and mirror it to get the whole? If you are registering off the edge, could it be possible that the edge is not correct? Just thinking out loud!

Try centering the machine on the centerline at the wide end, then doing a manual move to the Rhino dimensions to where the corners should be and check that with your laser. Again, just thinking out loud....hopefully some this thinking will help you find the issue.

BTW, what kind of machining strategy did you use in Madcam? Did you set your boundries with a region curve?

Mike

Mike I did not mirror my model along a centerline but I could do that. Might very well be the problem. I am machining useing planer finishing and using Blend in the settings. I also have a model sent to me from Joakim in Sweden. He added a top and bottom clipping plane but that didn't work either. I am really starting to think that it's the way I drew the model. Lots of things to try. Still green at this.

_________________
Beautiful and unusual tone woods at a reasonable price.
http://www.rctonewoods.com/RCT_Store
The Zootman
1109 Military Rd.
Kenmore, NY 14217
(716) 874-1498

I like Mikes advice.

One way to check you model is to draw a corner to corner flat surface above your fretboard model. You'll need to have your top view and either side or front view windows open. Highlight the flat surface, then nudge (alt down arrow) the surface downward in your front view while watching how it intersects your fretboard in the top view. It's a little like a CAT scan for fretboard curvature.

Thanks Sheldon I'll try that.

_________________
Beautiful and unusual tone woods at a reasonable price.
http://www.rctonewoods.com/RCT_Store
The Zootman
1109 Military Rd.
Kenmore, NY 14217
(716) 874-1498

Bob, I sent you an email with my info in it. Send me the model you used, as well as the desired dimensions of the fretboard. I will build a new one from scratch and compare it. If the original is wrong just use the one I build, but if the original is correct you will need to look at your machine set up!

Mike

Mike I will send it tomorrow

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Beautiful and unusual tone woods at a reasonable price.
http://www.rctonewoods.com/RCT_Store
The Zootman
1109 Military Rd.
Kenmore, NY 14217
(716) 874-1498

We have a digital dial indicator which goes into the quick change collet fitted to the spindle,

Even jigs which have been machined on the table when removed and refitted will be slightly inaccurate again,

Most of our jigs now have adjustment grub screws at the mounting points, so we can tweak the corners up or down accordingly

You need to clock your jig in or reface it for accuracy every time you remove and refit

Bob, for starters, check the machine for square and plumb etc. Have you run tests of squares etc. to measure to make sure it is calibrated properly?
Next, dump the HDPE as a fixture material. It is too unstable. Go with either a phenolic board or the material that Andy Birko is using. Whatever you use, you need to machine it flat, and carefully index it to your table.
Then, you need a really good way to reference the jigs so that you can get back to 0,0 precisely.

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I have been using MDF. It is a true spoilboard. It is cheap and you can resurface it if need be. I can get sheet after sheet of MDF from home depot until I get my setups down at which time might invest in the expensive stuff.

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Ken

How did it turn out Bob?


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Ken

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Ken

Well Ken as it turns out the fixture was not parallel to the "Y" axis. Made a new fixture out of MDF and all is well.

_________________
Beautiful and unusual tone woods at a reasonable price.
http://www.rctonewoods.com/RCT_Store
The Zootman
1109 Military Rd.
Kenmore, NY 14217
(716) 874-1498

Giod to know this stuff. Thanks


Sent from my iPhone using Tapatalk
Ken

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Ken