How to Make Your Own Delrin and Urethane Bushings


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We loved our new SPC Performance front upper control arms for our past project Nissan 350Z, but the bushings were SCCA-illegal as delivered.

It all has to do with the bushings on the inner pivots. SCCA Street Touring rules allow for alternate bushing material, so long as you don’t replace non-metallic components with metallic components. So you can replace rubber bushings with urethane or nylon or Delrin or some other non-metallic material.

Ah, but there’s another catch: When replacing the bushings, the ratio of metal to non-metal may not increase. Sounds like a real bull-crappy point, but it prevents a savvy builder from doing a full metal bushing with a thin layer of plastic and saying, “See? It’s legal.”

As you can see above, the bushings would never have passed muster as compared to the stock ones on the right. To be legal we’d have to build some of our own.

Step 1

Buy some Delrin. Actually, buy some polyoxymethylene, which is the chemical name for the thermoplastic sold by DuPont as Delrin (and by other companies under different names, such as Celcon, Ramtal and Kepital; it has no relation to Arby’s Beef ’n Cheddar.) We bought a 4-foot stick from Grainger for less than $50. It was more than enough for four bushings plus a few failed experiments.

Step 2

Call your dad* and have him build your bushings on his sweet lathe. Our dad is easy to identify because he’s always wearing pilfered GRM gear, but you may need a different ID method. Actually, machining Delrin is rather easy if you’re used to machining metals. Treat it a bit more gingerly than soft metals like aluminum or brass.

Turning speeds should be on the slow side because you don’t want to melt the plastic from friction. Start with shallow, slow cuts to see how your machine and tools react to the medium. Starting with 0.010-inch cuts at around 800 rpm should keep you out of trouble, and you can adjust from there if your machine is happy.

Of course, if you don’t have a lathe, it’s simple enough to drop off your control arms, your Delrin stock, and some dimensions at a machine shop and let them know what you want.

*Dad may vary in size, color and temperament. Consult your owner’s manual for more details.

Step 3

Install your fancy new legal bushings. Our Delrin control arm bushings were paired with some bronze-coated steel sleeves we got from a local specialty hardware store. The sleeves are the same dimension and wall thickness as the stock metal inserts, so we’re comfortable that we didn’t increase our metal/ non-metal ratio in our new bushings.

Step 4

Now we could take full advantage of our SPC control arms, with their eccentric, adjustable upper ball joints that gave us control over both camber angle and caster angle–two things not adjustable on the stock 350Z.

Pour Your Own Urethane Bushings

Not content with having built our own Delrin bushings by hand, we wanted to see if other materials would bow to our will. Specifically, we wanted to know if building urethane bushings was within the purview of the mortal automotive journalist–if so, then such a project could easily be tackled by a smarter creature, like the average autocrosser or track day enthusiast.

Turns out it is, with a few caveats. While we didn’t build any urethane bushings for our Z, we figured since we were talking about building bushings anyway, this would be a perfect place to share our findings.

Step 1

Although harder urethanes can be machined, most bushing-grade urethane is molded. This is a process you can do on your own with simple methods, but the trick is to produce a mold first.

Luckily we had the perfect candidate: the stock anti-roll bar bushings from our 1991 Toyota MR2 Turbo, a part that’s NLA from Toyota. Our bushings were dry and creaky, but complete enough to use for molds so we could duplicate them.

Step 2

Eventually you’ll want to get your new toy out of your mold, so your mold must be able to separate. To do this, you’ll need to build it in two (or more) pieces.

We used a cut-up Glad food storage container to contain our mold. We first cut out the bottom so we could have access to both sides. Then we packed Play-Doh into the bottom to form our temporary half-mold. Play-Doh makes a great temporary mold because it’s soft, it seals well, it works easily and, best of all, it’s inexpensive and available anywhere. We then pressed our bushing halfway into our half-mold, which half-filled our container.

If we molded the hole through the center of the bushing, we’d have to destroy the mold to remove our finished piece. The goal is to build a couple of these things, so that’s a no-go. We filled the hole with Play-Doh and we’ll simply use a hole saw to cut our hole in the finished bushing.

Step 3

A generous coating of mold release will let us separate our solid mold half from the Play-Doh and the bushing once it hardens. You can use a commercially available mold release, but liquid soap, hand lotion or water-based personal lubricants like K-Y Jelly will also work. Stay away from silicones and petroleum- based products.

Step 4

Now we pour our first half of the mold. We’re using simple, inexpensive plaster of paris. Plaster experiences almost zero shrinkage as it hardens, making it an excellent mold-making medium. The downside is that it isn’t the most durable thing in the world. A plaster mold has a somewhat soft, granular structure, kind of like a big block of sidewalk chalk. It’s a great inexpensive alternative if you’re only going to make a few copies of something. If you plan on molding several copies of an item, it’s best to go with a more durable mold medium.

Step 5

After a couple hours–maybe a bit longer in colder or more humid climates–you can remove the Play-Doh from the mold half. If you did a good job with the mold release, the Play-Doh should pull off pretty cleanly, revealing half of the item you’re copying and your half-mold.

Step 6

After another coat of mold release, you’ll be ready to pour the second half of your mold. At some point, you’ll also want to make an allowance for a hole so you can pour your liquid urethane into your mold. We found a little cardboard tube from a spark plug, packed it with Play-Doh, and used it to mold a channel in our second mold half. We’ll finish the hole with a drill later.

Step 7

Once the second half of your mold dries, you can separate it and remove your original part. You now have a cavity that you’ll use to mold your new pieces. We finished our pour hole with a drill and cleaned up some of the mold’s rough edges by hand before our first test.

Step 8

We got our polyurethane in the form of a 16-ounce kit from a supply house in South Florida for under $20. It’s a twopart mixture that takes about 10 minutes to start thickening once mixed and about 24 hours to cure to the point where you can remove it from the mold. Urethane hardness is measured on the Shore scale. We used a mix with a hardness of Shore 80. It’s about as hard as tire rubber and a little harder than your average rubber suspension bushing.

Step 9

To calculate how much liquid urethane we’d need to mix up, we asked our old pal Archimedes and simply dunked our old bushing in a graduated cup to measure its displacement. Beats doing the math.

Step 10

We taped up our mold and poured our mixed urethane. When mixing, do it gently and thoroughly. If you go too fast, you can introduce air into the mixture. If you see bubbles forming, wait for them to work their way out of the liquid mix before pouring. When you pour the urethane, do it slowly so it fills the cavity completely. Going too fast can trap air pockets inside.

Step 11

A day later, you can separate your mold and gently remove your new piece. You may have a few bits of “flash” that need to be trimmed– extra urethane that seeps into the cracks–but if you did everything right you should have a near-exact copy of your original.

Step 12

After trimming off additional material from the pour hole, we simply used a hole saw to cut our center hole. Go slow and it’s a much easier process.

Step 13

And there you go: one homecooked bushing. This simple, affordable molding method can be used to reproduce more than just bushings, too. Basically, you can use it to make a duplicate of any bit you may have. Just adjust your material hardness as needed for the job.

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Comments

View comments on the GRM forums
SVreX
SVreX MegaDork
6/6/18 3:21 p.m.

Or, you could machine them out of used cast-off bathroom partitions, like the Mumpkin!

Good article, JG!

DaveEstey
DaveEstey PowerDork
6/6/18 4:32 p.m.

Step one: Buy a lathe.


Great.

OnTheChip
OnTheChip New Reader
6/6/18 5:16 p.m.

Does the control arm motion occur between the bolt and sleeve, the sleeve and bushing, or busing and arm?

Dr. Hess
Dr. Hess MegaDork
6/6/18 7:44 p.m.

Delrin is good E36 M3.  McMaster-Carr sells it in smaller quantities. 

te72
te72 Reader
6/6/18 9:56 p.m.

Question, where did you order your dad from? He looks like a quality dad, so I'm guessing off one of those fancy tool trucks. The dad I found can be sourced from your local "knows way too much to be working behind a parts counter" guy. =P

 

Also, darn you Toyota, for making so many parts NLA for the cars that, you know, made your reputation among enthusiasts... I know the aftermarket serves most of these cars, and they were built fairly well back then, but hey, everything ages, things break. I'd love to be able to keep the old Yotas alive...

TurboFocus
TurboFocus Reader
6/7/18 9:39 a.m.

In reply to OnTheChip :

I would imagine that the rotating portion occurs mostly betweem bolt/sleeve and depending on design (like aftermarket kits) some will happen between sleeve and bushing.

the bushing is there for more than just the rotation such as bumps that jerk the arm around or load that the bolt/sleeve/etc cannot compensate for

 

thats my WAG

kb58
kb58 SuperDork
6/7/18 11:25 a.m.
DaveEstey said:

Step one: Buy a lathe.

 

Beat me to it. It's like that woodworking show that is/was on PBS, called something like "Yankee Workshop". Anyway, he'd produce fabulous furniture... using his $50,000 worth of equipment.

Driven5
Driven5 SuperDork
6/7/18 11:51 a.m.
OnTheChip said:

Does the control arm motion occur between the bolt and sleeve, the sleeve and bushing, or busing and arm?

Typically the sleeve rotates in the bushing and the bolt is just there to clamp it all together, but that's just the beginning.  In order for everything to locate, support, and move properly, you'll also need to figure out the fit between the bushing OD and the control arm housing ID, the amount of resulting shrinkage of the installed bushing ID, the fit between the sleeve and installed bushing ID, the fit between the bushing flanges and the mounting bracket, and the fit between the sleeve and the mounting bracket to ensure the fit between the bushing flanges and the mounting bracket when the bolt locks the bracket down tight against the sleeve. And that's all assuming that the suspension you're working with has already been confirmed as operating only pure single axis rotational motion for each bushing being replaced.

For all of the 'technical' articles/blogs/posts I have seen out there proclaiming how 'easy' it is to make (or have made) DIY bushings, I don't think I've ever seen one that includes any of the 'minor details' that are actually critical to doing so correctly. It always seems to be some variation on...

Phase 1: Collect Delrin

Phase 2: ?

Phase 3: Bushings

APEowner
APEowner HalfDork
6/7/18 12:38 p.m.

In most applications the sleave is clamped between the ears of the mount so that it can't rotate.  That's why factory bushings should be tightened with the suspension loaded.  If you don' then the rubber bushing is twisted at rest.  I've fixed some wonky handling issues just by taking miss matched pre-load out of control arm bushings. 

When I make Delrin bushings I like to do a press fit on the inner sleave and a light sliding fit on the outside of the bushing.  This makes for more bearing surface and allows for a grease fitting if you want one.  Sometimes the outer portion isn't a complete sleave (like in a leaf spring eye) in which case I make bushing a press fit to the outer portion and let the sleave rotate.

 

OnTheChip
OnTheChip New Reader
6/7/18 3:06 p.m.

In reply to APEowner :

This is my understanding as well. Stock rubber bushings allow arm motion by deflection of the rubber, which isn't possible with Delrin (or other 'hard' materials). If the length of the inner sleave doesn't allow a tight, clamping fit with the bracket, motion will occur between the bolt and sleave, which could also allow slop: ie. I'll handling.

To Driven5's point, details matter and tolerances/fit should be specified in these, otherwise useful, articles.

Ben_Modified
Ben_Modified HalfDork
6/7/18 10:02 p.m.
DaveEstey said:

Step one: Buy a lathe.


Great.

 

There are deals to be had. I paid $600 for mine and it has more than paid for itself (my wife's wedding ring alone). The person that I bought it from had just purchased a high end cad etc lathe and was making space in his shop. I took a look at it and told him I would take it.  His response....well, you would be a $#%&$ing idiot if you didn't. It took an engine hoist to get it out of the back of my scion xb.

Randy_Forbes
Randy_Forbes New Reader
6/9/18 10:19 a.m.

Fun projects!  I made a couple of forays into bushing making__machined and molded__some years back with good results.

Before Jeff Ireland/Ireland Engineering started marketing his urethane subframe mounting bushings for the E-30 esque Z3 and M Rdstr applications, I was molding some "bushing stuffers" from a pourable Devcon 2-part urethane (Shore hardness unknown, as I've slept since then...).  These filled the longitudinal voids in the OE bushings and also packed the space at the tops and bottoms to eliminate a substantial amount of the excessive compliance.  By all accounts, they were a success.  The professionally manufactured and store-bought polyurethane bushes from IE were a substantial improvement on what I was making, so I abandoned them and have probably purchased and installed Jeff's bushes in 150-175 cars since then.  I wish I could remember what album has the pictures of my molds (made in 2-pieces from a pourable aluminum/resin product from Loctite).  I'll edit this post if I come across them, but I too used a plastic food-container dish to make the molds!

The machined bushes were turned in both UHMW (Ultra High Molecular Weight bushing material) and a bronze alloy.  I never finished the bronze ones to size, opting to install the UHMW ones for a test first.  They are still in the upper/outer pivot position, allowing a decrease from +1* (positive) camber to approximately -2* negative camber on my '57 Healey.  I made them eccentric, so that they were adjustable to enable matching both sides.  Given that the UHMW bushes have been in for nearly 15 years already (recently inspected during a front shock upgrade) and found that there's still no perceptible wear at the ends or bolt-holes and that the bronze bushes only need (both of) the ends trimmed to size, I doubt I'll need to make any more for this application in my lifetime!

 UHMW bushes before ends were trimmed to size

Fitted to the Healey's upper trunion (previously machined for straight bore; original 1/2-bushes were tapered)

So yes, Doable AND Fun project that anyone can do at home**
 

 

 

** NO Dads were used or otherwise harmed during the above exercises. 

Knurled.
Knurled. MegaDork
6/9/18 10:28 a.m.
DaveEstey said:

Step one: Buy a lathe.


Great.

Heh, that was my exact response as well.

 

Now, having a lathe is awesome, if you have the space.

clshore
clshore New Reader
6/9/18 10:37 a.m.

In reply to Dr. Hess :

Delrin can also be had impregnated with Graphite or Moly, to provide self lubricating properties.

alfabeach
alfabeach New Reader
6/12/18 7:51 a.m.

Could you 3D print them easier?

jkstill
jkstill None
6/12/18 1:03 p.m.

I bought a 9x20 lathe a few years ago for the express purpose of making delrin bushings.

The new offset bushings in the front upper A-arm now  allow -3.0 degrees of camber, which was not previously possible.

Messing with the design a bit allowed forcing the A-arm back a bit further in the mounting brackets, providing more caster as well.

Since then that lathe has come in handy for many other projects.

 

APEowner
APEowner HalfDork
6/12/18 2:22 p.m.
alfabeach said:

Could you 3D print them easier?

3D printing is getting better and better all the time but I think the tolerances that a good bushing needs to be held to are a bit tight for at least the home machines to hold.

jkstill
jkstill New Reader
6/12/18 3:55 p.m.

In reply to APEowner :

I know someone that has used this same attribute of stock bushings to affect corner weighting in SCCA classes that do not allow these parts to be substituted.

 

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