Ripples in my moulds

[heli_bee]

Hi Guys,

I need some help from the experts!!

I have been maching some MDF moulds for a model that a friend has designed. I am using a home built Rockcliff Model A, Mach3 to run it and Vectric 3D to generate the G-Code for the moulds.

Iam currently using a 10mm Radius Bit for the rough cutting and a 3mm Ball Nose for the finishing cuts.

The rough cutting seems to be fine, (800mm/min, 3mm pass depth and 33% stepover, cutting along the X-Axis) see photo IMG_2991.jpg.

The finishing cutting (800mm/min, 1.5mm pass depth and 9% stepover, cutting along the Y-Axis) seemed to leave some ridges, which I put down to using a Radius Bit for the rough cuts.

I gave the part a number of good epoxy resin coats, using a hot air gun to wick the resin into the MDF, until I ended up with quite a bit of excess resin on the surface - more than enough to fill the ridges.

I re-ran the finishing cut and have ended up with more ridges - see photos, IMG_2992.jpg and IMG_2993.jpg.

Does anyone have any clues as to what is causing them? Is it the 3mm tool flexing? Is the feed rate too high? Could the part be moving slightly on the machine bed? Is it something else?

Please help,
Martin.

[ger21]

Could be a mechanical issue, like a loose setscrew maybe.
I use a 1/8" ballnose bit at 150-170ipm (3800mm) with glass smooth results. If anything, you're feedrate is on the low side.

[heli_bee]

I just zoomed in on the Cut3D preview and can see what appear to be the ridges.

Any ideas as to what settings I might need to change in Cut3D to stop these ridges?

Regards,
Martin.

[heli_bee]

Just had a look at the original Solidworks .STL file.

I think I can see some ridges there as well! Now I'm really out of my depth, how do I get round this problem?

[ger21]

I guess I wasn't sure what you were talking about. You need to change your SolidWorks .stl export tolerances to get a smoother finish.

[Markwind]

As Gerry mentined the STL looks like it needs better precision, in solidworks after clicking a save as, STL the pop up window will show an options button, you can set the precision higher before exporting the STL,

[heli_bee]

Markwind,

I will give it a go. I was thinking I was going to have to wade through the instructions, and online, to find out how to adjust the settings.

You have just saved me a lot of time. As soon as the wife has left for the post Christmas sales, I will give it a go.

Many thanks,

Martin.

[heli_bee]

Time for the next installment of this Xmas story!!

Well the designer of the moulds, and I, have had a play and have wound the resolution of the .STL file right up. It has now gone from 43KB in size to 559KB. No ridges are visible when displayed in SW or Cut3D.

I ran the finishing cuts again using the updated, larger, .STL file as a starting point, but to no avail. I still have ridges in my mould. I tried the finishing cuts in the X-Axis, in the Y-Axis and at a 45 degree angle. All had ridges.

I am now somewhat stuck. Is it a software issue or a mechanical one?

I have spoken to the designer and he is happy for me to post the Canopy Mould .STL file on the forum. What we are hoping is that there is someone out there that has the time, and spare capacity on their machine, to convert it to G-Code and cut a test piece. If ridges appear in their version of the mould then the problem is with the software, if no ridges are present, then it must be a mechanical issue with my machine!!! (The part is only 187mm by 70mm by 52mm).

Is there anyone able to help out?

Martin.

P.S. This is also posted on RCGroups.

[mcphill]

When you cut in X compared to in Y, are the ridges in the same direction? If not, then it is the scallop of the tool making the ridges. To get rid if it, you need to decrease the size of your stepover. If you use a 1/8" ball end mill, your finish pass should be done with a stepover of around 0.002" if you want a very smooth finish. You would do well to do the final pass in multiple directions, as well, for the best finish.

[Senna]

One additional thing to insure is that your cutting table/surface is perfectly perpendicular to your router shaft/cutter axis.

Steve

[heli_bee]

mcphill,

The ridges stay in the same direction, regardless of which way the cutter travels. It is almost as if the MDF had extra hard layers within it!!

Senna,

The machine is as perpendicular as I can get it (about 98-99%) - if I have to rebuild the Z-Axis I will try to get it even better.

Regards,

Martin.

[Markwind]

After re-reading your message
Quote "The finishing cutting (800mm/min, 1.5mm pass depth and 9% stepover, cutting along the Y-Axis) seemed to leave some ridges"

Sorry, for not looking at this in the first place, but after doing some math, using a 1.5mm deep x 9% stepover of a 10mm cutter is much too coarse for a fine finish,

I primarily work in inches, and for a smooth finish in wood, you need anywhere from about .002"to .010" inch stepover in all directions
Which would translate in metric to about 0.05mm to 0.20mm (if my math is correct)

It going to take longer to cut but you should see a much improved looking part