Delrin Collets.

[Raymond AndersonParticipant @raymondanderson34407]

Hello guys,

I have recently been thinking about making emergency collets from Delrin, based on the ER style only with a larger gripping size than my ER40. [up to a Ø of around 42mm] they would only be used for light finishing not roughing. I will also make the chuck to suit the collets. Any thoughts on the use of Delrin for this application?

Regards,

Raymond.

[Raymond AndersonParticipant @raymondanderson34407]

[Roger WoollettParticipant @rogerwoollett53105]

I think you might find it will not grip the workpiece very well. Delrin is slippery stuff.

Roger Woollett

[Raymond AndersonParticipant @raymondanderson34407]

Roger,

I forgot about the "slipperieness" of Delrin, [I suppose that one of the reasons that some feedscrew nuts are made from it]. Maybe Nylon 66 would be a more suitable material? Or even Rigid PVC? My thinking is to bore the collet in the chuck until the part just goes in snuggly, then the final tighten up. As mentioned it would only be light cuts / loads.

Regards,

Raymond.

[John Stevenson 1Participant @johnstevenson1]

No reason why not, they already make emergency collets for 5C in Nylon and Brass for this reason.

[Raymond AndersonParticipant @raymondanderson34407]

Thanks John, I have now only to decide between either, Glass filled Nylon 66 [ERTALON 66 GF30] or NYLATRON GSM which is a cast grade of Nylon 6. both seem to have the properties needed.

Regards,

Raymond.

[Jeff DaymanParticipant @jeffdayman43397]

Nylatron may also be too slippery – some grades have friction modifiers, as Nylatron is often used for gearing.

I'd stick to brass or plain nylon for emerg collets if I were you. Plain nylon is a lot cheaper than Ertalon or Nylatron usually. Glass fibre fill will not increase the grip much, if that is what you are after, but it would increase the clamping strength of the plastic.

JD

[Raymond AndersonParticipant @raymondanderson34407]

Hi Jeff, The increase in clamping strength is desirable through using any of the 2 I mentioned.

Hopefully they should not be too slippery. I have ordered a short bar of each to test out. . There would appear to be a load of different engineering plastics out there with vastly different properties. I will also conduct a test on Rigid PVC [it may well prove to be as good in this application as any of the others mentioned].

Regards,

Raymond.

[Jeff DaymanParticipant @jeffdayman43397]

PVC may work fine Raymond, but it melts at a fairly low temp. If your cuts are very light you may be OK but if the work gets hot your collet may melt. This is true for most plastics, but PVC will be worse than nylons.

I also worry about outgassing of nasty chemicals from PVC. Many plastics moulders in North America will not mould it anymore due to toxic vapours released when PVC is melted for moulding. The melt off-gases are very corrosive and will rust steel several metres away. The vinyl chemical which is the main component in PVC is one of the most toxic chemicals around in its' free state, before polymerisation. Fine outdoors or underground, but I don't want any PVC indoors in my house or shop.

JD

[Raymond AndersonParticipant @raymondanderson34407]

Jeff, thanks for the info re, Rigid pvc. I have decided to stick with the 2 that I mentioned earlier

I will decide exactly which one, once I have tested both types.

Best wishes,

Raymond.

[Michael GilliganParticipant @michaelgilligan61133]

Raymond,

Personally, I would suggest using PEEK … It's a superb engineering plastic, and well worth keeping some in stock.

PEEK used to be very expensive; but ebay seller benchrisseb has oddments available from time to time. [no connection, except as a very satisfied customer]

MichaelG.

[Raymond AndersonParticipant @raymondanderson34407]

Thanks Michael I did originally think about some of the advanced engineering plastics like PEEK TORLON and PPSU but at the price they would not have been economical for my home needs.

I checked out your link he has some PEEK but none in a large enough Ø for my needs and yes the prices are very good , so I have noted him for future reference.

Best wishes,

Raymond.

[Sam StonesParticipant @samstones42903]

Hi Raymond,

Before delving into this topic more deeply, I would certainly recommend testing. There have been many instances when I either ignored or didn’t comprehend what might happen.

Fundamentally, you are dealing with elasticity and creep, and how they change with temperature. On top of that there is also the question of friction.

That said, there are many properties involved when considering an application in plastics materials. I seem to recall `discovering’ that there are something like sixty-four essential properties even before considering the effects of fillers and polymer blends. A number of these properties have already been mentioned in the above posts.

Suffice to say that several properties are interrelated to some degree. For example, rigidity varies with temperature. The trouble with this is that there is seldom a straight-line relationship. Some materials gradually soften while others suddenly `let go’. That would take us into the realms of crystalline (eg. Delrin and nylon) versus amorphous (eg. PVC and PS), which may be interesting but take up too much time here.

Of significance in terms of making collets (or other devices for clamping [load-bearing]), are the following thermal and mechanical properties.

Thermal conductivity, often overlooked in various processes.

In the case of a collet, let me suggest that most plastics will offer little to no heat-sink effects which you would experience with say brass. The surface temperature of a plastics collet where it contacts the workpiece is what matters, and where melting could take place quite rapidly.

Melting (softening) point/temperature. HDT or heat distortion temperature is often used to determine suitability. However, these properties are usually obtained at a standard temperature, but have little bearing on the overall response to variations of temperature.

In terms of load bearing, (as in clamping via a collet), there are two interconnecting properties which I mentioned above; ie. elasticity and creep. The former property is readily understood, whereas creep can creep up on you (boy what a pun). Filled plastics also creep to varying extents, depending of course upon the type and quantity of filler.

I would be taking great care when machining filled materials, especially glass and other hard fillers. Particles can get in and under slide-ways, and can instantly jam the mechanism. I found this out from experience when my ML7 saddle jammed solid. The filler in this case was glass bead, and took hours to remove even after a complete saddle strip-down.

Without a data sheet, I’d be out of my depth with the fairly modern, and more exotic materials. I’ve also been `out of the game’ too long. AND, I tend to yack too much.

Good luck,

Sam

PS Unfortunately JD, your house and shop are surrounded by PVC. It's the insulating stuff on your wiring, but that's another story.

Edited By Sam Stones on 21/12/2012 22:09:24

[Jeff DaymanParticipant @jeffdayman43397]

"PS Unfortunately JD, your house and shop are surrounded by PVC. It's the insulating stuff on your wiring, but that's another story."

Actually it isn't. My house wiring is done with rubber jacketed industrial wire. The original owner specified that it not be PVC insulated and not be aluminum conductors. (These were the current fad when house was built, and the aluminum wire proved disastrous in North America) . But, you are correct in saying most if not all modern house wiring is PVC insulated. Cheap, works, but not very safe chemically. There will likely be a study at some point that offgassing from PVC and from breathing fumes from cars ahead on the highways are the leading cause of cancers, in my opinion. Oh well, can't live in a glass dome. Life itself is risky.

JD

[John Stevenson 1Participant @johnstevenson1]

Raymond,

It's not rocket science, just make a collet and try it out. What do you have to loose ?

John S.

[Sam StonesParticipant @samstones42903]

Hi Jeff,

My apologies! I shouldn’t jump to conclusions.

Best regards,

Sam

[Sam StonesParticipant @samstones42903]

Raymond,

Sorry to use up your thread for this partially(?) OT.

I could imagine that `plasticiser migration’ would form part of an investigation agenda, as would knowing the main source of the stuff which coats the inside of a (largely new) vehicle windscreen.

What a tin of worms for (us) rocket scientists.

Regards,

Sam

[Chris TriceParticipant @christrice43267]

Posted by John Stevenson on 21/12/2012 22:28:53:

Raymond,

It's not rocket science, just make a collet and try it out. What do you have to loose ?

John S.

Yes, tighten that rocket science Raymond. (runs and hides).

[Raymond AndersonParticipant @raymondanderson34407]

Sam, Thanks for the very informative post on the plastic's debate ,they seem to be a subject all on their own [ now if only I were an Industrial chemist it would be a whole lot easier ]

John, Yes, I am going to use the 2 types that I mentioned earlier, either 1 should be suitable for my needs. I will make them the same style as ER ones only larger, and using 4 slits front and rear .

Thanks to everyone for the input.

Regards,

Raymond.

[Ian S CParticipant @iansc]

The heat conductivity problem might be overcome by using one of the metal impregnated plastics. Ian S C

[jim bothParticipant @jimboth37830]

Posted by John Stevenson on 21/12/2012 22:28:53:

Raymond,

It's not rocket science, just make a collet and try it out. What do you have to loose ?

John S.

well said! i once built a poppin engine, lacking any cast iron i used leaded bar, everyone told me it wouldn't work! they were wrong………….

[Ian S CParticipant @iansc]

Jim, why would it not work?, My flame licker has a cylinder made from some scap steel, it's reasonably easy to machine, so by me its OK, and I used cast iron for the piston. Ian S C

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Raymond ,

(1) Just use one of the industrial grades of Tufnol . Rigid , easy to machine and its use for collets , chuck jaws and other gripping devices in industry is well proven .

(2) Almost all materials have a whole raft of material properties – the engineers skill is in deciding which ones are relevant .

(3) If using any of the Nylon class materials you may well meet problems that arise from the material properties but not in any obvious way . Just to give one example – when cutting the relief slots with a slitting saw the slot will often close up and grip the saw .

(4) Some plastic materials don't like water based soluble oils and other cutting oils – they tend to absorb it and swell .

Regards ,

Michael Williams .

[jason udallParticipant @jasonudall57142]

Posted by MICHAEL WILLIAMS on 23/12/2012 10:15:43:

Hi Raymond ,

(1) Just use one of the industrial grades of Tufnol . Rigid , easy to machine and its use for collets , chuck jaws and other gripping devices in industry is well proven .

(2) Almost all materials have a whole raft of material properties – the engineers skill is in deciding which ones are relevant .

(3) If using any of the Nylon class materials you may well meet problems that arise from the material properties but not in any obvious way . Just to give one example – when cutting the relief slots with a slitting saw the slot will often close up and grip the saw .

(4) Some plastic materials don't like water based soluble oils and other cutting oils – they tend to absorb it and swell .

Regards ,

Michael Williams .

Nylon in particular..

Nylon horrid to machine..meaure twice after machining if close tolerences required

Teflon machines well doesnt melt…swarf/burr tends to be fluffy

PVDF..see telon

PVC..machines well , can melt.

Pelathane…rubbery..

ABS..great..smells bad good stability

Peek…Crystline..Yes I know lots of grades but all crystaline

polycarbonate..ok but acts crystaline

Acetal./delrin….simular.. machines well acetal smells of cat pee

Acetal "emergency" collets 5C definitly available

Tufnol…GET the RIGHT type…grain direction

Why not use standard collet and split bushes for range top hat shape say

[Sub MandrelParticipant @submandrel]

If you have the time and some EN24T or similar why not make 'proper' collets?

Neil

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