custom reamer for plastic needed

surplusjohn · Nov 5, 2020

I have a problem with a new rotationally molded HDPE part. if you have ever worked with rotational molding then you know that tolerances are problematic. anyways, we could not avoid designing a fitting that relies on a consistent ID, vendor thought they could do it, but they cant, so i have to come up with a simple way of machining the ID. This is a step fitting, tapered id for female fit to vacuum hose cuffs. Major ID is 2.45 " the minor is 2.3 range. we would be removing up to .060 of the diameter max.
question is, do such beasts exist? a long shot. or does anyone here make such things?
alternately, i have to figure out how to make a reamer for plastics. I am thinking of something that looks like a 3 blade spade bit, i can laser cut pre-hardened steel and grind a negative rake on the edge.
BTW, work holding is always a problem with these parts,

it seems that the molder should be able to route this, but they don't seem confident that it will work, so I am looking at alternate solutions just in case.

i am pretty good at designing around the short comings of rotational molding, but you cant always avoid going straight down the angry hole.
thanks

TeachMePlease · Nov 5, 2020

These guys made me a run of custom HSS reamers and they were good to deal with and made a nice tool. However, my reamer was 2.95mm, not sure if they go up to your size, but it couldn't hurt to ask:

Reamers, Piloted Reamers, Threaded & Chucking Reamer, Reamer Sets | Aircraft Tools

Limy Sami · Nov 5, 2020

John, a pic of the part and a few dimensions would be a great help, as my experience with plastics has taught me they don't always do what you want or expect them to.

CAMasochism · Nov 5, 2020

Limy Sami said:
John, a pic of the part and a few dimensions would be a great help, as my experience with plastics has taught me they don't always do what you want or expect them to.

Opposite of my experience, I can easily predict what my reamers will do. If the hole is dimensioned .500 +.0005 -0 and I use a .500 reamer it will ream under sized. If it is dimensioned .500 +0 -.0005 it will ream over sized. EVERY DAMN TIME.

AARONT · Nov 5, 2020

Can you get away with a 2-5/16" reamer? https://www.mscdirect.com/product/details/02322204

LockNut · Nov 5, 2020

surplusjohn said:
I have a problem with a new rotationally molded HDPE part. if you have ever worked with rotational molding then you know that tolerances are problematic. anyways, we could not avoid designing a fitting that relies on a consistent ID, vendor thought they could do it, but they cant, so i have to come up with a simple way of machining the ID. This is a step fitting, tapered id for female fit to vacuum hose cuffs. Major ID is 2.45 " the minor is 2.3 range. we would be removing up to .060 of the diameter max.
question is, do such beasts exist? a long shot. or does anyone here make such things?
alternately, i have to figure out how to make a reamer for plastics. I am thinking of something that looks like a 3 blade spade bit, i can laser cut pre-hardened steel and grind a negative rake on the edge.
BTW, work holding is always a problem with these parts,

it seems that the molder should be able to route this, but they don't seem confident that it will work, so I am looking at alternate solutions just in case.

i am pretty good at designing around the short comings of rotational molding, but you cant always avoid going straight down the angry hole.
thanks

I see no reason this can't be routed and routing should be the way forward. I worked for a rotational molder for about a year and they were more than capable of this and did it on a constant basis. Fixturing might be problematic but necessary. We did replacement parts for Boeing aircraft where new parts were scarce, like the FA-18 and older aircraft.

petersen · Nov 5, 2020

Depending on your rate of taper; that sounds like an NPT pipe thread reamer.

Unfortunately, it sounds like your diameter falls between 2"NPT and
2-1/2" NPT.

You might have a cutter grinder reduce a 2-1/2" NPT reamer to your
size and taper.

They are commonly available in a "back-spiral" style which would
work best.

petersen

DocsMachine · Nov 5, 2020

Just spitballing here, but I have to ask: Can the part be turned?

That is, whip up a set of soft jaws for a lathe chuck- aluminum would be sufficient, I'd think- and turn the ID to whatever taper you need? A CNC would of course be ideal, but even a manual lathe with a good taper attachment should be able to do it.

Making a set of soft jaws would likely be easier- and cheaper- than trying to make a custom reamer.

Make wide "pie slice" jaws, and turn them to nearly the exact OD of the part, and you shouldn't have to worry too much about distortion.

Doc.

surplusjohn · Nov 6, 2020

Doc, good point, the part could be turned, but i dont think the vendor has that capability. but if i was going to turn it i would use an internal skiving tool. probably not the way it will go, but spit balling is always worth while.

routing with a draft bit seems to be the obvious way, but they are trying to avoid that for some reason. I am often in the position of having to second guess a vendor. I like to respect our vendors' skills, giving them the benefit of the doubt that they know what they are doing, but at the same time I am reading tea leaves to try to anticipate what they are missing or simply have wrong. when i dont do that i get in trouble. Several months ago on a different project, i had a part that i wanted to die cut but was doubtful that it could be done so effectively, the vendor said no problem, even when i pointed out my concerns. 2 months later they said no way will this work. that required a design change that made a major change to the product's appearance which caused marketing changes, etc. So i tool them at their word but the vendor just didnt give it any thought.

Peter from Holland · Nov 6, 2020

If the bore is not all the way trough perhaps on a valve seating machine ???
We need a drawing to see if possible

Peter

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custom reamer for plastic needed

surplusjohn

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Limy Sami

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CAMasochism

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AARONT

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LockNut

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