Need advice for correct "plastic" to use

IronReb · Apr 6, 2018

I was given a sample to quote that is a mounting bracket for a Pulse pump..no idea what a pulse pump is.
It is 3/8 thick, 5" x 5", four 3/8 holes and a 1" hole in the center with (4)3/16 holes around the center hole.

It is shiny white plastic looking but is very stiff, not much give to it at all being 3/8 thick and about 5" square.

I am sure it is not UHMW because if it were I could bend it easily?

Would nylon be a good choice?

If so, is there a certain grade you would suggest?

Bobw · Apr 6, 2018

Delrin.. ASS-a-tel..

EVERYTHING should be made out of Delrin. If it needs to be stronger 2000 or 7000
series aluminum... If it needs to be shinier and heavier, 303.. If it needs to
be stronger 17-4.. If you want it to rust 12L14.. No other materials are necessary. :crazy:

CHEAP.. PVC.. Pretty stiff.. LDPE isn't bad and pretty cheap, fairly hard and stiff.
They both machine quite well, and aren't *squishy* so you can actually hold 'em.

I'd rather try machining a wet piece of bubble gum before UHMW, that stuff sucks, and it
seems to melt somewhere around body temperature.

tnmgcarbide · Apr 6, 2018

i suppose it depends how hot the pump gets, if that's an issue.

stiff, white plastic alludes to polypropylene, which is cheap and easy to machine. you could likely use anything
that's similar unless there's an issue with heat, chemistry , etc .

delrin is great , but is more expensive than some other plastics = overkill.. and would eat into your profit on the work. 6/6 nylon , pvc , polypro , acetal , acrylic.....likely all would do fine.

why not ask the client?
is there a callout in the bill of materials on the print?

IronReb · Apr 6, 2018

tnmgcarbide said:
i suppose it depends how hot the pump gets, if that's an issue.

stiff, white plastic alludes to polypropylene, which is cheap and easy to machine. you could likely use anything
that's similar unless there's an issue with heat, chemistry , etc .

delrin is great , but is more expensive than some other plastics = overkill.. and would eat into your profit on the work. 6/6 nylon , pvc , polypro , acetal , acrylic.....likely all would do fine.

why not ask the client?
is there a callout on the bill of materials in the print?

There is no print or bill of material. This makes me nervous not knowing the exact application it is used in and the customer has no clue either, he has been ordering from OEM I suspect.

IronReb · Apr 6, 2018

I think I will go with Delrin...would rather go with overkill and lose the bid than put something out there that may fail and smear out company name.

tnmgcarbide · Apr 6, 2018

"There is no print or bill of material"

i hate those jobs.

better safe than sorry- can you get a "stocking fee" or advance retainer, upfront, for materials .
it sure would suck to make 600 of them.....only to have some dickhead engineer suddenly wake-up and
say "oh ...sorry this plastic has to be ________(food grade , non-electrostatic, dielectric, proven to not cause
cancer in the state of california...) and kill the order, leaving you with 100# of doorstops.

azmachining · Apr 6, 2018

Except for it most likely isn't delrin, rather HDPE. Which is way cheaper.

azmachining · Apr 6, 2018

Cheapest poly I know of and is good $#!t.

IronReb · Apr 6, 2018

azmachining said:
Except for it most likely isn't delrin, rather HDPE. Which is way cheaper.

HDPE?

See, this is why this F ing job makes me wake up at night...not knowing WTF this material is and making the wrong choice and carrying 100% of the blame if it goes to shit.

azmachining · Apr 6, 2018

Sucks, customers like that are a pain.
White HDPE sheet has a real hi gloss finish. I have a stack of 12"x12" or so 1" thick sheets setting here I could post a photo of if that helps.

azmachining · Apr 6, 2018

If they are HDPE and you bid delrin and any one else knows it you will most likely lose it.

azmachining · Apr 6, 2018

Although you may not want to deal with them anyway... Not know is a liability as has been said and of it were me I would not leave ANYTHING blank or to speculation.

tnmgcarbide · Apr 6, 2018

i would just go with the acetal . of all the plastics , it machines the nicest and won't cause any headaches.
poly-e is soggy and springy and doesn't like to be clamped . your part is flat and relatively thin,
and delrin is more dimensionally stable than most plastics.
i don't know how you plan to fixture this piece, but if the delrin will work-use it.

Bobw · Apr 6, 2018

IronReb said:
HDPE?

See, this is why this F ing job makes me wake up at night...not knowing WTF this material is and making the wrong choice and carrying 100% of the blame if it goes to shit.

Its F'n plastic.. don't sweat it.. If it mattered it would be metal.
HDPE, High Density Poly Ethelyne (I think, and spelling). LDPE is low density.

HDPE is the stuff that your milk jug caps are made out of.

Look on the bright side... If it fails.. You get to make more, and make more money... If it
doesn't. You don't get to make more, and you don't get to make more money.

Its PLASTIC.. Make it out of something white and plastic and call it good. To give yourself the
warm and fuzzies, get your customer to approve the material choice. HDPE is a good choice, its CHEAP,
which means that is probably what the original part was made out of.. The only thing cheaper is PVC, but
its grey (at least from McMaster Carr).

If its really an issue, have your customer send the sample out to be analyzed.

azmachining · Apr 6, 2018

Last time I checked pvc was more, but that that's not from McMaster and it was gray I think.

azmachining · Apr 6, 2018

Just DO IT! Or pass it along to me, I will, love me sum plastic.

Bobw · Apr 6, 2018

azmachining said:
Just DO IT! Or pass it along to me, I will, love me sum plastic.

I love me some plastic too, as long as its not Teflon or UHMW... Or glass filled.

Spruewell · Apr 6, 2018

Have the customer source the material. Then all you have to worry about is meeting dimensional specs. If he cannot/will not source material, have him help you pick one and sign off on it

IronReb · Apr 7, 2018

After much thinking and reading your post on this matter, this is where I lay on it...

Our salesman that brought this into the shop will need to carry some of the load by finding out exactly what this part does, the temps involved and chemicals it is exposed to, once this has been determined I will give the info to my local plastics supplier and go with his recommendation, once that has been done I will pass it off to our salesman who will either get his customer to sign off on it or bare the full responsibility on his back, be damned if I am going to say "this" will work and take the heat if it fails.

Pattnmaker · Apr 8, 2018

What I typically do in a situation like this is to quote it both ways. Give them a price for cheap poly and a price for the Acetal or delrin. If they ask whats the difference send them data sheets that you get from your supplier or online.

This way the customer has made the decision rather than you. It also makes them question the lowball guys price who also only quoted the cheapest material. If the more expensive option is still considerably cheaper than the OEM part they may want to go with the expensive option. If no one shows what the difference in costs are the easy thing to do is just go with the cheapest supplier.

Need advice for correct "plastic" to use

Stainless

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Diamond

Stainless

Stainless

Diamond

Cast Iron

Cast Iron

Stainless

Cast Iron

Cast Iron

Cast Iron

Diamond

Diamond

Cast Iron

Cast Iron

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