Machining Nylon

Pop it in the oven for 2 hours @ 80deg before you start. This will drive out some of the moisture in it and will actually make it a little bit harder and less likely to tear, giving you a smoother cut. You can let it cool for a couple of hours, you don't have to machine it straight out of the oven. Toothpaste works well for a final polish if you don't the part smelling minty fresh

Peter

Scary sharp HSS tool, with a nice radius on the cutting edge tip.

Fairly high rpm, and use the power or auto feed for a steady cut.

A couple thou per rev feed should be fine.

A hook to catch theh swarf and draw it away from the chuck and the part, is a good bet, but nothing sturdy enough to hurt yourself, if it gets tied up on the swarf and flogs around.

Nylon machines quite nicely. Sharp tools!

Cheers Trevor Jones

I only machine Delrin (acetal), it machines nicely. I use the finest feed for a finishing cut & then polish with a polishing mop loaded with jeweller's rouge if a really fine polish is required - however the 0.0018 feed does leave a nice finish on my ML7T.

Adding to your tips: Don't try to make slight cuts. You'll end in just rubbing the work. Depth of cut 1mm or more. Keep the tool cutting. A constant stream of chips is the key for a good surface. If you stop feeding, retract the tool. If you don't do that, work will melt and the surface is ruined.

Nick

OK guys and Karen, thanks for the advice. I will give it another g

tonight.

Peter - Put it in the oven at 80 degrees??? Are you sure? I'd hav though freezing it would have been better, but I will try it anyway!

What tool geometry is required? HSS, but what profile is best? I a making a 32mm diameter mandrel for winding carbon fibre on, so I nee to perform some kind of polishing/smoothing operation because I can have any grooves remaining (if I did, I would never be able to get th cured carbon off the mandrel!).

Cheers,

Garth

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It's to get the humidity out of it. Let it cool down afterwards.

Sharp! Geometry for Al is OK. I feel it doesn't make that much difference as long as it is sharp. A relatively huge radius seems to make better results. Tip radius 2mm or such. But you need some mm for minimum depth of cut. It's best to try to get the right diameter with a test-cut and then do the cut in one go. And did I say that the tool has to be sharp?

Nick

No, it makes it easier. You can machine to almost any size, then alte the temperature to make the bar fit.

Maintaining the temperature accurately afterwards is the problem. :-)

Robi

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I disagree! It would be virtually impossible to maintain a very high o very low temperature during the turning process itself without living i a fridge or an oven!

Cheers,

Garth

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As Nick said, the reason is to remove some of the moisture content from the material. Commercially we dry the nylon pellets/granules for

The reason is that Nylon 6 and 66 are extremely hygroscopic and will absorb up to 5% of moisture by weight. The water molecules slip into the gaps between the longchain polymer molecule strands allowing them to move and generally be more flexible in relation to each other. As such, nylon with a high moisture content is both more flexible and softer, although tougher than a dry nylon.

You get dimensional change too, as a 'wet' nylon will grow slightly in size.

Peter

You should speak to your local plastics supplier to get advice too - they are handling this type of question all the time. Most cities have quite a number of plastics suppliers.

I use Delrin as previously stated, machines very well, takes very heavy or light cuts (.002 easily done with a sharp tool) and is suitable for medical purposes - it can be sterilised in an autoclave. Water is not a problem for this material, and can be polished to a mirror finish if needs be.

.... a quick related question on the plastics topic, ..... from a relative plastics-noobey.

We were given a box of bits'n'bobs of offcut plastic bar in various diameters. About 90% of it is is black; ... and to someone who has spent their 50- odd years on this planet so far working with metals, they all look the same.

Is there a simple way of telling nylon from delrin and anything else that might be mixed in this box? (short of assessing each for their specific gravity).

I used a piece a few months back (which I thought was Delrin) but it now appears that it may be a type of nylon (or somesuch) as the finished part has 'grown' about 3% or so since being put into use and is now binding the pivot that previously it was bearing smoothly.

Ian

Well Polypropylene and Polyethylene both have an SG of around 0.9, so pieces of this should float in water.

Acetal - get a match/lighter and hold it to the end for a few seconds, then blow out the flame and sniff it. if the ensuing effects are similar to tear gas in that you nose stings and your eyes water, then it is Acetal (Delrin is a band name for Dupont acetal).

Doing the same with Nylon just smells like burnt plastic.

Polystyrene is easily dissolved by acetone, so splash a bit of the wifes nail polish remover on and see what happens

Clear plastics like Polycarbonate and Acrylic - hit them with a hammer. If it dents slightly it's probably PC, and if it shatters it's probably Acrylic .

Peter

Snipped loads of terrible typing. I can spell really, I just can't type very well.

Peter