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Discussion Starter · #1 · (Edited)
Pic 1: Hoisting the machine on the stand with a come-along, one-man (careful) job Jan
Pic2: First 16 production parts in 0.75 thick HDPE plastic, made some changes on the way, placed individually and I screwed up 3.
Pic3: Using 27x48 (quarter sheets from 54x96 HDPE Starboard, which fit nicely next to the lathe option) I will nest and machine 24 parts in the second panel. The interior ring is a 2-point to 6-point connector, otherwise it's waste material.

Question: I like to engrave/mark all parts in this second panel with a 20 character text string (solid line option), but found that V-bits are really for engraving and not fine enough for part marking. I will try a 1/16" or 3/32" straight end mill next, 1/4" shank diameter so I don't need to change the collet. I am thinking .10 to .16 text height, and maybe 0.04-0.08 deep. It's on this 3-dog plastic handle and the user should not feel the marking.

Any advice on this kind of part marking and what bits to use?
 

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David - Machinist in wood
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Looks good, Paul. How does the HDPE machine? How long did it take to cut all of those? Bit, feed, speed, etc.?

Can you use a smaller V bit? I realize at the very tip of a 5/8" diameter V bit it's the same as a much smaller V bit but I know Fusion 360 treats the larger bit differently because of the overall diameter, so maybe the software you're using does the same thing.

David
 

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Discussion Starter · #3 · (Edited)
Thanks, David. HDPE machines easily, no burning, no melting, no plastic buildup on the cutter, although it always generates a massive amount of fine shavings. On this first panel I did not use the dust collector as I wanted to see the cutter at all times. I will on the second panel.

I used Onsrud 65-020 and 65-021 3/16" upcut bits 1/4" shank, at 19000 spindle speed and 70ipm feedrate.
Each part takes about 23 minutes, with the interior ring with the 7 holes nearly half of that, holes are slow, and mostly 3 or 4 passes for 0.75" part thickness.

Lettering on plastic parts: I never worked with V-bits and/or engraving before. I used 60deg V-bits, maybe I should use 30deg bits. But the shape of this bit just does seem right to me to produce fine single/solid line markings. I tested various depths using these V-bits. I'll try the 1/16 and 3/32" straight end mill next, if that does not work I'll take another look at V-bits. I use VCarve Pro (and also Draftsight for geometry construction work).
 

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Looking good so far, Paul. One thing about using the dust collector is that those plastic shavings may generate a good static charge/attraction. Make sure your dust collector hose has a grounded wire running through it.

If you are using Vcarve you might try doing the text with the 60 degree V-bit, and using the VCarve toolpath. Not on single line text, but using a font with some internal area. The characters don't have to be big or bold to still work.

4D
 

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Discussion Starter · #5 ·
So far no real progress in exploring (plastic) part marking.
The straight 1/16 and 3/32 bits don't give me nice enough lettering for the various single line fonts I tried. I also used 'text along a curve' and that VCarve Pro option works well.
I agree I need to pursue V-bits more as they produce better results. I'll order a 30 deg V-bit next (instead of the 60deg bits I have) and see if that gives me acceptable results, both for single line and true font lettering, for 0.20 and 0.25" letter height.
Any additional advice is appreciated!
 

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The VCarve option in VCarve Pro, using outlined fonts rather than single line fonts may give you nicer more readable text. It will make sharp corners when needed by lifting the v-bit up as it enters a corner. Steeper bits create more readable text as they typically are more in shadow when the part is out in the sun and held vertically.

To speed up your profile cuts you might experiment with fewer passes (deeper cuts) and even faster feed speed. I made a mistake yesterday using a 3/16" upcut spiral in baltic birch plywood. The cut was supposed to be a very shallow 1/32" deep pocket, but I forgot to set where Z=0 was and the initial cut started roughly .4" deep. Surprisingly the hole was clean and the bit didn't snap. There is plenty of sharp cutting edge on the sides of most bits that never gets used unless you do deeper passes.

4D
 

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Discussion Starter · #8 ·
I did a variety of tests engraving 'uturnhandles' on HDPE thermoplastic using 11, 30 and 60 deg V-bits using Solid Line and True font options, and Text and Vcarve toolpaths. Text height varied from 0.25 to 0.40inch. 100s of combinations possible, way too many to try! So far 60 deg V-bits, true font, Vcarve toolpath looks best for approx. 0.35" letter height but still feels a little bit rough on top. I'll try a small burner on various marks and see if it improves. I stay away from sanding as I found that sanding HDPE always leaves marks and scratches. I also have damaged handles with an extra groove at the edge and see if the burner makes those acceptable too, i.e. good enough for use, maybe not good enough for sales.

For roundover edges I use a separate benchtop router and use 5/16 roundover bits for the peripheries on 0.75 thick parts. As the spoilboard (two) and the HDPE sheet all vary slightly in flatness/thcikness over the sheet, I cannot do the roundover edges on the CNC machine. If I do, the edges do not come out uniformly nice.

I'll keep you posted if the 60deg V-bit + burner touchup will do a good enough job. The larger the lettering the better it looks so simple conclusion is that using a CNC Nebula may not be very good for small letter engraving. However I have no experience with professional engraving so there may be other ways/bits/speeds that work better.

Examples on scratch HDPE
 

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