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Old 03-08-2017, 04:55 PM
kjoiner kjoiner is offline
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Default Ideas for making a part from UHMW

Hello,

We make this part in house and are currently making it from strip stock UHMW. The part is rough cut to length, drilled in a drill jig, countersunk, then finished with a router. There are several steps to this and one request I have from our production staff is a way to make this on the Stinger. Cutting it from sheet stock would be attractive if I could ensure the material lays flat on the table. I don't have a vacuum table but there may be some other fixturing that would work. The material is 3/16" thick. Another question is finding an 82 countersink router bit. Most I've seen are 90 and I'm pretty sure a standard countersink would melt the plastic. Any thoughts?





Thanks!

Kyle
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Old 03-08-2017, 07:04 PM
Pete Cyr Pete Cyr is offline
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https://www.amazon.com/Countersinks-...3A82%20Degrees
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Old 03-08-2017, 07:57 PM
mike.davison mike.davison is offline
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So...... the experienced folks may have a better answer, but here's a thought. Lay out a table-sized job with multiples of this part separated by areas for hold-down screws every N parts (you'll have to decide how closely to place the hold-down screws). Then, clamp the stock from the edges (away from where said hold-down screws will go), run the first job to drill the hold down holes. Then, put screws in the hold-down holes and run the second job, which mills the desired parts, connected by an onion skin and/or tabs. Then pop it off, cut the parts apart, quickly clean up the edges and collect your bonus for being so smart.
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Old 03-10-2017, 07:58 AM
kjoiner kjoiner is offline
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Hello,

Thanks for the responses. My main concern with countersinks is that since I'm running a Milwaukee router, I don't want to risk melting the plastic when countersinking it. Those options may still work.

I've started setting up the layout in V Carve. I'll probably order some UHMW sheet in the near future and try out the ideas. It might be worthwhile for me to make a jig that I can locate on the main spoil board. The jig could have T nuts on the bottom side so I can use machine screws to secure the sheet stock in a repeatable manner.

Kyle
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Old 03-10-2017, 01:40 PM
mike.davison mike.davison is offline
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On concerns about melting plastic while countersinking: Use the Drilling Toolpath, a slow spindle speed, a higher retract gap.... You can do it! :-)

A jig with T nut hold down points is a great idea.

You could probably also do nearly all the milling, leaving an onion skin perhaps, then come back with a final pass to remove all but a tiny tab on the end of each part. This would minimize the chance of parts getting damaged due to movement and would eliminate nearly all post cleanup.
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Last edited by mike.davison; 03-10-2017 at 01:51 PM.
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Old 03-10-2017, 02:49 PM
Kyle Stapleton Kyle Stapleton is offline
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How exact do these need to be? A table saw, chop saw router table would be way faster getting them to size. I would just use a cnc for the holes and the sinks, by making a jig to hold multiple parts at one time.
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Old 03-10-2017, 04:09 PM
rcrawford rcrawford is offline
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You might be better off doing the countersinks at the drill press, if you only have a router on your Stinger.

I would try using a double sided tape to hold the sheet in place. Drill all the holes, then use a 3/16' roundover bit to cut the profiles and round them over at the same time.

This is where a pressure foot would be nice. A little double sided tape and a pressure foot would allow you to cut the parts completely out without tabs or any other hold down method.
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Old 03-11-2017, 06:52 AM
Ger21 Ger21 is offline
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Imo, that part would be much faster the way that you're currently doing them.
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Old 03-13-2017, 08:42 AM
kjoiner kjoiner is offline
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Hello,

Going back to my original process, I need to make a slight correction. We currently buy the UHMW in sheet stock. They shear the sheet into strips, cut the strips to rough length, drill the holes, countersink the holes, then carry the strips over to a jig and use a roundover bit with a ball bearing pilot to create the rounds. There is a lot of carrying material around from one process to the next. Part of the deal for me to have the Stinger for R&D work is to find areas where I can use it to do some light production work.

I plan to ask for a time study to see how long it takes them to make the parts for a comparison to using the Stinger. I like the idea of a pressure foot, but this also might be an opportunity to explore a vacuum fixture - something like the BradyVacII. I'm thinking of using a 24" x 24" sheet.

Time wise, the toolpaths I've created in V Carve seem long. What are the suggested feeds and speeds for UHMW? right now I've set it to 70 ipm but that seems slow.

Kyle
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  #10  
Old 03-13-2017, 10:02 AM
rcrawford rcrawford is offline
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The parts are a little small for a vac table - not sure they would stay in place; pretty narrow pieces, so not much holding power with vacuum. You could make a jig using a rubber mat to increase the friction and create a better seal, but I still don't think those narrow pieces will hold well enough to give you smooth cuts.

I think you might be better off with a few strips of double sided tape (just enough to add friction to the pieces so they don't move laterally) and a pressure foot.
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