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Old 02-25-2022, 05:53 AM
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Density worked. Took some measurements, did some weighing .. all my materials came out to the expected products within about 1% error.

Lots of UHMW as expected, some PTFE, and couple of 1/2" thick 4" wide, 18" long sheets of Delrin, and one nice 12" x 6" x 1/2" sheet of Ketron Peek. Surprised, about $1000 worth of exotic plastics (at McMaster prices) .... most of that stuff came from people that donated it cause they know I make a lot of projects, or scrap that I picked up at auctions.

Already laminated the density chart to go in my shop info binder

Shame the Delrin is in 1/2" sheets, would be a pain to machine into bushing.

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Old 02-25-2022, 03:40 PM
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Density worked. Took some measurements, did some weighing .. all my materials came out to the expected products within about 1% error.

Lots of UHMW as expected, some PTFE, and couple of 1/2" thick 4" wide, 18" long sheets of Delrin, and one nice 12" x 6" x 1/2" sheet of Ketron Peek. Surprised, about $1000 worth of exotic plastics (at McMaster prices) .... most of that stuff came from people that donated it cause they know I make a lot of projects, or scrap that I picked up at auctions.

Already laminated the density chart to go in my shop info binder

Shame the Delrin is in 1/2" sheets, would be a pain to machine into bushing.

Good work! Glad it helped you sort your stuff.

Which way are you leaning?

IMO, any of those would probably work fine but I'd go with stronger/tougher because of the probable dirt and dust.

Delrin is a standard "go-to" for bearing surfaces but you were concerned about temperature. I think it would be OK personally but the PTFE and PEEK will definitely be more heat-proof. The PTFE is super slippery, inert, and temp-stable but I'm not sure how it would behave coated with sand.

The PEEK is high-tech. I'll bet it was expensive! It probably would be best for a bearing if carbon- or even PTFE-filled but even unfilled PEEK should be "slippery enough" for your bushing. PEEK may "out-wear" the other options if dirt is present as it is super tough. PPS is a similar material and I remember it being VERY wear resistant.

Thanks for sharing this latest project.

Mike

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Old 02-25-2022, 04:49 PM
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I think I'm going to try the Delrin ... I'm thinking with the 1" steel shaft it in it's unlikely to hit 180 degrees .. if it did it probably means something is on fire

Looking forward to machining it, ordered a 1 5/8 OD rod. Still might try to come up with some kind of seal for it, there are thousands of 1" seals out there.

Thanks again for the suggestions.

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Old 02-25-2022, 04:53 PM
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I am a little late seeing this thread.

Johnny, I have a few pieces of varied types of plastic pieces some rounds and some bars left over from past and repeat jobs that may work well for your project. If any of these pieces will work better than the materials you have on hand I will contribute to the effort.

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Old 02-25-2022, 07:29 PM
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IRT Heat and Delrin.
Quite a few aftermarket upper A Arms using Delrin bushings located adjacent to the exhaust manifolds.
Just sayin'

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Old 02-26-2022, 03:28 AM
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Dmorg ... hold on to that large OD stuff, it's got to be close to the cost of silver by weight. Appreciate the offer but I think I'm all set.

OG, I think you are correct, I don't think I've ever reached into an engine compartment and had any piece of metal except the engine and the radiator burn me.

Got in some Nylon 6/6 MDS filled today ... jeez that stuff is hard. I'm going to have a nice collection of materials to make ... you know ... whatever

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Old 03-01-2022, 06:00 AM
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Final product on the far right. Jeez, this Delrin is like machining metal that isn't metal, like if your most cutest and nicest little sister was metal, that's the way it treats you.

Makes pretty manageable swarf compared to most plastics, easily machines with carbide inserts, starting with large OD drills no problem with pecking and some WD40, surface finish is super nice, and I could easily take off 0.001" at a time unlike some plastics that want you to take more of a bite if using anything other than razor sharp HSS.

Also more dimensionally stable, doesn't distort while machining, chuck doesn't distort it much (assuming you don't over tighten). I perused a few forums for tips on machining it, and more than one person said it's their favorite material to machine and if at all possible to make something out of Delrin instead of metal that's what they'll do.

Below ... OEM bearing, UHMW Polyethylene and Delrin on the right.

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Old 03-01-2022, 07:25 AM
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Quote:
Originally Posted by dataway View Post
Final product on the far right. Jeez, this Delrin is like machining metal that isn't metal, like if your most cutest and nicest little sister was metal, that's the way it treats you.

Makes pretty manageable swarf compared to most plastics, easily machines with carbide inserts, starting with large OD drills no problem with pecking and some WD40, surface finish is super nice, and I could easily take off 0.001" at a time unlike some plastics that want you to take more of a bite if using anything other than razor sharp HSS.

Also more dimensionally stable, doesn't distort while machining, chuck doesn't distort it much (assuming you don't over tighten). I perused a few forums for tips on machining it, and more than one person said it's their favorite material to machine and if at all possible to make something out of Delrin instead of metal that's what they'll do.

Below ... OEM bearing, UHMW Polyethylene and Delrin on the right.

Interesting. I thought Delrin was always white. Machining is just part of my job though. I'm not a journeyman. We mainly use UHMW and Nylatron here. See Delrin sometimes. Looks good though!

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Old 03-01-2022, 08:49 AM
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According to McMaster the only difference is that white is FDA approved and meets ANSI 61 (no lead) specs. I assume they offer it in black as solely an aesthetics consideration.

Did some more reading up on it and it comes highly recommend for industrial environments, oils etc. with temp limits being it's only drawback.

Can't wait to come up with something else to make with it. Look forward to trying it out on the milling machine.

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Old 03-01-2022, 09:30 AM
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Johnny,

Another task completed and well done. Thanks for sharing.

Delrin is a trade name of DuPont "likely the largest manufacturer" and is an Acetal Copolymer.

Natural and Black colors are the most common but there are a few other colors available.


Dave

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Old 03-01-2022, 10:38 AM
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Thanks again for sharing and glad to see your success.

The finish looks great. I expect it will work out well for you.

As to color, there are many versions of acetal (POM) available for molding. I don't know what is commonly sold in "stock" shapes.

The colors often follow the fillers, and the fillers are used to modify for specific properties. Black could be a graphite-filled version, which would be marketed for bearing applications.

Way back, we would use blends with PTFE fillers for machine bushings. I recall spec'ing "Delrin AF" but that was when DuPont probably owned the market. Yes, I'm a dinosaur.

Here's a good description of the material and why it is a "workhorse" for product designers. I think the list of different grades is interesting:

https://omnexus.specialchem.com/sele...ne-pom-plastic

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Old 03-01-2022, 01:50 PM
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McMaster-Carr offers most of the variations. The type I purchased has some kind of filler for wear resistance .. doesn't specify what. They also offer the AF, and fiber reinforced varieties.

Their description: "Because these naturally slippery, wear-resistant rods and discs resist expanding when exposed to heat and moisture, they can be easily machined to close tolerances. They are a good choice for parts that require precision, such as gears, bushings, and bearings. DelrinŽ acetal resin is also known as acetal homopolymer; it is stronger and stiffer than acetal copolymer."

They also offer Acetal Copolymer as a "economic alternative" to the Acetal Homopolymer .. and various types and fillers for that too

I opted for one of the more affordable versions of the homopolymer Delrin, instead of the PTFE filled Delrin ... which is in the area of $70 / foot in the size I needed.

Yes, quite the rabbit hole when you start looking at plastics.

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Old 03-01-2022, 03:00 PM
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Wow! $70/ft for a cylindrical stock sounds crazy.

I'd be right there with you buying a lower cost material.

I'm not calibrated but that's a deterrent to machining plastic parts as a hobby!

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Old 03-01-2022, 03:08 PM
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This thread prompted me to take a look at the bearing on my car since everything's apart right now. I replaced the lower bearing with an NOS unit about 15 years ago and the mileage has been minimal. I didn't look at it closely back then and just kind of popped it in. I see what you're saying! That bearing is pretty crude. I'm really surprised with the amount of play in it. I could hear the grit in the ball bearings, so I cleaned it really good and repacked it with grease. It's better now, but I'm really surprised how sloppy it is.

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Old 03-01-2022, 03:22 PM
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They are very proud ($$$) of the "plastic" materials.

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Old 03-01-2022, 05:25 PM
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Hehehe .. yep, I could get high grade tool steel in the same size for less money.

I think that lower bearing is an afterthought because so much of the feel at the wheel comes from the upper bearing ... which is the same type... but two of them back to back.

One thing to check if you ever have your columns apart that far is ... is the bearing actually doing anything. As I mentioned, both these columns seemed to feel pretty good ... but not one of the four bearings in the both of them was actually rotating, they were all acting as bushings with the shaft just spinning inside the inner race. Including the nice column from a 56K mile car that was properly stored.

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