Liquid nitrogen will most likely split the puck. The outer surface in contact with the LN2 will shrink quicker than the inside.
In lab we used to amuse ourselves by throwing rubber stoppers in LN2 and watching them split
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Probably dry ice would suffice.
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Dry ice it is. That had to be fun at work !!!
I will start with the house freezer and work my way down .
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I cut 1/4"wide slots in hockey pucks for plexiglass sneeze guards, freezing wasn’t required, compressed air was a plus. You generate a bunch of rubber dust. I did them with my little Sieg X2 CNC mill, so I’ll have to wait till I get home to see what the feed rate was that I used.
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I was thinking more like just a freezer, get it down to around 0°. That’s all they did with the tires.
Let us know how it goes. 
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It has been done before by someone on the forum, see the post further down in that thread for endmill used and speeds.
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I bought pucks and did a lot of searching to find milling rubber is a process in itself.
I am waiting for an 8mm collect for the McFly tool because I never surfaces the MDF.
I was originally thinking to mill all sorts of stuff, now I am thinking engraving ( somehow ) and some rub and buff .
I did find this link talking about using needles for cutters. Comments ?
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I had good luck with a sharp 22 degree or 30 degree V-bit for engraving pucks. Spray paint had been used for the larger quantity, but it tended to flake off in some areas while engraving…I think in part because I froze the pucks overnight. Rub n Buff should have a great result I think!
You might need to play with speeds and feeds a bit. I think I based mine off of acrylic S/F.
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That looks great ! Thanks for the information . I can’t wait to flatten my table and give this a try.
What RPM, Feed rate, DOC, Step Over did you use ?
I guess they were pretty close to default settings. I had used a 60deg V-bit, but would recommend at steeper one. Settings:
DOC: 0.1 in
RPM: 18000
Feed: 45 ipm
Plunge: 12 ipm
I didn’t tweak the stepovers but here’s the values:
Clearance stepover: 0.27 in
Finish Stepover: 0.02 in
I think I remember trying to speed up the feed rate, but wasn’t too happy with the resulting cut.
First cut, not as scary as I feared. Temperature was 21 F, I tried room temp 60 F as no real difference in chips/crumbs.
I tried the Rub and Buff.
The grooves are small, getting the paste into the grooves not easy. Used a lot of material.
I may have to deepen some cuts.
Should I let it dry before removing excess ? I tried to wipe down and that just smeared and pulled material out of the grooves.
I found that 120% of 35 ipm worked better, smoother cut surface.
| Tool | Vcarve Text | Contour Stars | AdV outRing | Adv inRing | ||
|---|---|---|---|---|---|---|
| 302 | ||||||
| DOC | inch | 0.03 | 0.02 | 0.012 | 0.012 | |
| FEED | in/min | 35 | 35 | 35 | 35 | 120% |
| RPM | 18000 | 18000 | 18000 | 18000 | ||
| Time | min | -2 | -2 | -2 | -2 |
Debris field.
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Tried Talcum powder and a rattle can poly acrylic. Not a good poly finish.
Rub and Buff salvage.
I think I need PATIENCE ! I found that 220 paper on palm sander removes DRY product. I will not use acetone to clean, I think it merges product into the rubber, dilutes the product in the groove which gets wiped out while trying to clean surface.
I noticed the bottom of the groove had debris. I used a dental tool to clear the cuts.
It takes the talcum powder much better.
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I did not like the detail of the small features.
I changed from a 60 deg VCarve bit to a 1/32 end mill and I shorten the time in ramping to reduce melting.
Puck is 20 F out of the house freezer and it makes a difference with the end mill.
| 122 | |||
| DOC | 0.03 | ||
| FEED | 30 | Ran at 120% | |
| RPM | 18000 | ||
| Ramp Angle | 10 | Reduced cut time | |
| Ramp Rate | 10 | ||
| Feed Rate | 10 |
The end mill produced anywhere from mush to small chips or strings.
The final solution was a close up vacuum. I tried air blow and that seemed to push the material back into the grooves.
The process is out of freezer and cut with vacuum.
Use a dental tool to clear grooves. I have a fair amount of flash to trim. I tried sanding it out and lost edge detail before the flash cleared.
The VCarve bit clears bigger chips. I now realize I need to scrap and recut as a normal process.
The back side will have the player name and number. I am going to use the VCarve bit because the features are larger.
Now hopefully I can sand the Rub and Buff off the high side. I am trying that patience concept and letting it dry.
It takes a bit to get the grooves filled and I have to tape the outside cylinder so I don’t have to clean off the Rub and Buff on a cross hatched surface.
Final test part. Give it a clear acrylic coat and good to go.
I need to fill grooves better. I think the material rolls like mortar that is too dry.
It’s wax based so I am going to try heat to settle the material.
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I have had this idea for a while now. Y’all gave some great info.
I made progress in quality and repeatability engraving the pucks.
In short I used a Harvey 2 flute bit #957631, this was after buying a single flute bit, asking a question and finding the single flute will not plunge. Oops.
I found this article understandable. The simple examples helped.
The Harvey tech Dan was very informative. He sent these recommendations ( with appropriate disclaimers ). So I used the following parameters to make the Tool path in Fusion
957631
| Application | RPM | IPM | Chip Load | SFM | Radial DOC | Axial DOC |
|---|---|---|---|---|---|---|
| Slotting | 10,000 | 18 | .0009 | 81.7 | 100% Cutter Diameter | 50% Cutter Diameter |
| Plunging | 10,000 | 9 | .00045 | 81.7 | 100% Cutter Diameter | 50% Cutter Diameter |
I used these parameters.
The runtime is 19 minutes with a few minutes of easy dental work.
The “chips” were strings of material that largely got sucked up. The bit does collect material at times. The material would work it’s way up away from the cutting action.
The process of clearing debris was minimal except for a few things.
The outer ring did not clear at all and and the first “E” in EASTERN is a problem.
NOTE: Do the dental work when there are hot off the press. I just did 5 that had cooled and the effort was significantly more.
The solution for the outer ring was to increase groove width so it took three paths to clear the area.
Here are the examples. I fixed the outer ring, not the “E”. You can see the path difference in ncviewer . You can also see the other E has a better path . No clue.
My conclusion is to have features more than 2 tool diameters. This also removes most flash issues.
This text also requires dental work and some flash issues . Note the single pass paths.
I have to make 15 pucks ( 11 cut, may redo a few ) .
The other side will be a 90 deg vCarve, Let’s see what that brings.
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Using the #301 90 deg bit, I was able to get good Vcarve cut using a chipload of .0025 ( per some acrylic posts ) 10K rpm @ 50 ipm .
The max depth in the Name is 0.037 . The max depth in the Number is 0.106
I found it worked to cut the depth in half to get a good bite. This left the surface finish better than a single pass or lighter passes. There was still rough surface, some debris hanging on the sides and the bottom of the groove.
For cleaning runs, I tried increasing IPM runs, but that just hurt the surface finish as it when faster.
So I used 18K and 10 IPM and it cleaned and fixed ( melted ) the sides nicely. Sweet ! I may go higher RPM.
There still is some light wire brush/dental work, but not bad. The surface sealing is noticeable.
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Rub and Buff notes on rubber.
Small grooves are a challenge.
I tried a hair dryer to melt the material into the grooves, which did not work as well as expected.
The rubber takes the material quickly. This means that sanding may remove detail even when careful.
So I tried petroleum jelly on the rubber ( high surfaces ) first, then added the Rub and Buff.
That allowed me to wipe the high surfaces of %70 of the material, but it still left a sheen of material on the rubber.
I tried hand sanding with 320 grit sand paper which did not work, 220 grit worked better.
I ended up using a pad sander with 220 grit with light pressure. The rubber dust goes into the grooves, so you need to vacuum that out ( looks like you lost detail ).
I did not have the patience to let it dry completely before sanding which made some of the rubber dust to stick to the Rub and Buff. Damn lack of patience !!!
I added a single coat of PolyAcrylic clear satin which shined up the sanded surfaces.
Now the complete process is set ( unless I change my mind again ).
I have a lot of hours left to complete the project, but I am satisfied with the results. The thrill is almost over, now it’s time to slug it out.
.
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On projects where I use rub-n-buff I thin it just a bit with mineral spirits. This helps it get into diamond drag engravings on granite and to easily spread with a rubber roller (Brayer) for coloring only the tops of v-carved and painted items. The surface of the granite cleaned up well with a rag dampened with mineral spirits.
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