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I want to use my woodworking power tools and make flat curved parts up to approx. 10 inches in size/diameter and 7/8 thick from very strong plastics. These should never break, are held/handled as standalone items by people and have a rather smooth but NOT supersmooth/supershiny appearance to make handling comfortable but not slippery. I need something low cost and stronger than Finnish multiply. I am thinking of nylon (very strong but seems really too expensive) or UHMW-Polyethylene or any low cost plastic I can machine myself, or as a last resort request a contractor to do it with CNC machining. All the parts will have 1/4, 5/16, 3/8, 7/16 or 1/2in rounded edges (roundover). Any recommendations? Thanks.
 

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I have used very cheap cutting boards from homeware stores as material on my boat. Cheaper than ply and no maintenance.

It saws, drills and files like wood. I have not routed but I power planed the stuff.

Not 7/8" thick though.

Tks
C ya.
 

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I've machined UHMW on a milling machine and it cuts like butter. If you use a router I would slow it down as much as possible. I don't know how it will react at those speeds.
 

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Discussion Starter #5
Thanks for the responses. I got a small sample of .75 nylon and 1.0 UHMW today and it machines amazingly well, I would say better than hardwood. It's a little bit dangerous in smaller holes/cutouts as the router bit sometimes nearly grabbed into the plastic. Maybe the router bit is getting dull.

They told me that CNC machining of these plastics is done at very high speeds to avoid local melting, at much higher speeds than woodworking tools. I did not know if that was true but I took it very easy anyway just to be sure and had the router bit remove only a little layer at each pass and never stayed at one spot or redid the same area within seconds. The sides and edges all came out fine.

However there is a problem: the roundover edge to flat transition is never smooth. The lines are all noticeable and can be easily felt and there is no way to sand them smooth I think. I hope I don't need a chemical to polish these transition lines smooth (or other areas of the part when needed). Any solution or recommendation?
 

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"Any solution or recommendation?"
******************
Don't use a bearing on the work or templet.
& if you must, isolate the work such that nothing can move.
Moreover, neither the templet nor the work can express any millmarks or chops.
Workpiece control & fixture rigidity cannot be compromised, lest the chatter you're experiencing. Requires lots of homework to overcome, has taken me years.
**********************
 

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Discussion Starter #8
What are Corian cutouts?
"Don't use a bearing on the work or templet"??
Can you explain: no bearing, no template? I am using both, on a benchtop table router.
I think your point is that chatter, vibration, slight motion, etc., will lead to inaccuracies and unsmooth transitions. However I am thinking that with woodworking tools I can never get a perfect part, e.g. due to small surface problems, roundover edge problems, small template damages, etc., etc. . So I am trying to find out if there are good ways to IMPROVE a plastic part after machining (as you can do so perfectly with wood by sanding).
To hand machine a part perfectly
 

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Trade the bearing for a collar guide-bush system.
It does not turn and does not vibrate.
Its lateral force loads are transferred to the subbase not the cutter/armature system.
Don't use a bearnig guided cutter. Comprende?
 

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Quillman nailed it perfectly. All of that stuff machines very easily. Most of my invention prototypes are used to make injection-molded plastic parts. Heat is your enemy - if you will keep that in mind, you'll do okay. Corian was asked about above - it machines just as well, but can get overheated also. Polymeric products are best machined in quick movements with plenty of cooling time in between. I don't know what you call it, but I have some small hand-held tools in my shop that are used to provide fillets on edges of plastic parts. It works great, costs about $10.00; but don't expect perfectly smooth everywhere - it ain't gonna happen without some very skillful work with a hot torch and this is something I can never get satisfaction with - unless one particular employee is doing the work. With him it becomes perfect, with me it gets kinda drippy!
 

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If you want to use Corian:

Route at 30" per minute with a guide bearing. If your template is well finished and your bit is sharp, you will need almost no sanding. I know that it seams counter intuitive but a slow feed rate will heat the material less. Unlike many of the materials discussed, Corian can be sanded and polished easily. Do not try to heat polish it.

I know that the OP wants the material to grip well. Corian actually grips best when polished.

For all of the information you need on working with Corian see my website.

I hope this helps
Ken
 

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Discussion Starter #13
Thanks for pointing out Corian. It looks very very interesting.
The tensile and flexure strength even look OK but I am worried it may still be kind of brittle. Any experience with dropping a piece on concrete or dropping a heavy tool on an edge? If it is OK I also need to compare it cost-wise with parts machined from Nylon or UHMW.
 

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Just a small edging tool - it is about the size of a lumber crayon and has interchangable tips that form the desired radius - kinda like shaving.
Corian works wonderfully, but yes it is more prone to breakage than the UHMW or PE's.
Ken (above) is exactly right about its finishing characteristics - very nice material.
 

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Deburring Tool?

Just a small edging tool - it is about the size of a lumber crayon and has interchangable tips that form the desired radius . . . "

OPG3, are you describing 'Deburring tools' with interchangeable, carbide tips?
 

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Discussion Starter #17
Machined and tested Corian solid surface material

I machined two parts from Dupont Corian 1/2" thick and fastened them together into a 1" thick curved part. Then did some strength testing on 2" wide strips 1/2" thick and on this part also. It machined extremely well and very clean with a small woodworker's benchtop router and drill press, and I really liked it. However my fear was justified. As this is mainly used for countertops and similar applications with underlying support, I was afraid it would be too brittle for my standalone small curved parts and it is. If you drop the part on concrete by accident, it will break depending on how and at what angle and spot it hit the concrete. So it is by no means a tough material.

However I like the easy and clean machining of this type of material so much that I want to pursue this some more. I checked Wikipedia's entry for Corian and found many competitor materials mentioned. I am hoping that a few of them are much tougher than Corian.
Has anybody found a tough soild surface material among Meganite, LG-HI-MACS, Marlan, Staron, Gibraltar, LivingStone, Durasolid, Kerrock, SOLIDEX, etc., as mentioned in Wikipedia under 'Corian'.
Thanks.
 

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Corian

Vandoom2,

Just some notes on Corian.

  1. I do not think you will find a solid surface product that is tougher. there are many that are more brittle
  2. When they made it in 3/4" it was tested with a .357 magnum from 15 feet, without failure.
  3. If you did not sand the piece smooth, you left stress risers in it (like scratches in glass). This may have been the cause of breakage.

I do not know the shape of your piece but it may be better to heat it and bend it to shape. This can anneal the Corian and make it a little harder and tougher.

I hope this helps
 

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Thanks for the responses. I got a small sample of .75 nylon and 1.0 UHMW today and it machines amazingly well, I would say better than hardwood. It's a little bit dangerous in smaller holes/cutouts as the router bit sometimes nearly grabbed into the plastic. Maybe the router bit is getting dull.
Probably not that bad - UHMW and PU (polyurethanes) in particular are very "grabby" so try to reduce the cut to the bare minimum (i.e. less than 1/2 the diameter of the cutter you are using) and avoid climb milling with a hand router at all costs

They told me that CNC machining of these plastics is done at very high speeds to avoid local melting, at much higher speeds than woodworking tools. I did not know if that was true but I took it very easy anyway just to be sure and had the router bit remove only a little layer at each pass and never stayed at one spot or redid the same area within seconds. The sides and edges all came out fine.
On CNC routers you aim the do the first (roughing) pass to within something like 0.1 to 0.5mm of the finish size and this pass is done at high feed speed, but relatively low spindle speed, e.g. for UHMW-PE 1000 grade something like 6 to 12 metres feed rate, 12,000 rpm feed rate on a 20mm diameter tool. This will generate a stream of tight curl chips rather than dust and therefore you don't get churning of waste in the cut which overheats and dulls bits. A second, finishing cut is then required because all plastics compress and spring back when cut and in addition the surface formed by the roughing cut isn't the best. Clearing swarf on the second pass can cause problems so vacuum extraction is recommended. Weld back is a phenomenon associated with nylons, acrylics and polycarbonates - it doesn't really occur with UHMW-PE.

However there is a problem: the roundover edge to flat transition is never smooth. The lines are all noticeable and can be easily felt and there is no way to sand them smooth I think. I hope I don't need a chemical to polish these transition lines smooth (or other areas of the part when needed). Any solution or recommendation?
You could try to find a cutter manufacturer who sells a roundover bit with a transitioning edge to the cutter, i.e. one which tapers out of the radius. We have one manufacturer here in the UK who does these, Titman, but they aren't cheap because they are industrial tools. As Patrick says bearing cutters always vibrate a little which isn't a problem on wood where you can sand afterwards, so guide bush and plain cutter is a good approach.

IHMO few plastics take to being sanded, although Corian and other solid surface materials are very good (as are acrylics). The problem is that most plastics tend to compress then spring back too easily under cutting/sanding (it's called polymer memory) - but you can often scrape plastics (card scraper) and some respond to a heat gun, e.g. acrylic and polycarbonate, but I've had variable/limited success with UHMW-PE and nylon/Delrin. One thing you mention is that Corian is brittle - it will chip if droppen on edge onto a concrete floor. I think pretty much all the countertop materials like Corian will be the same (and I've used several, e.g. Formica, Wilsonart, LG, Staron, Iro, Schock, etc) because they are acrylic polymers or co-polymers and acrylics are hard but brittle. As to its' strength, though, it is not the norm to back countertops over their entire width/length with sheet materail unless you are surfacing with 3mm (1/8in) or 6mm (1/4in) solid surface stock because such a backer will tend to bow very very quickly if not fixed down straight away. What we tend to do is to make up countertops from 12mm (1/2in) solid surface material with a 20mm (2in) wide strip of MR-MDF glued along both edges and the ends (silicone sealant) and then build the drop edges by adding another strip of 12mm stock. That makes for a strong and durable countertop which won't move so much

Regards

Phil
 

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A Corian cut out would be the scrap left over when they cut out a sink hole or other waste from making counter tops. Corian is a man made product. You can see it at places like Home Depot on their counter tops. You work it with routers and saws. It can be sanded and shaped pretty easily.
 
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