This is related to a project I'm working on.
I need to enlarge the hole through a control arm bushing to 13/16. I'm guessing it's NOT as easy as just grabbing a 13/16 bit and having at it.
What can I expect?

If anyone has any suggestions or tips on how to go about this, I'd appreciate it.

[This message has been edited by Raydar (edited 08-15-2012).]

I think you'll find that it will drill pretty easily. Soft enough to drill, hard enough to not be difficult (like rubber would be).
~ Paul
aka "Tha Driver"

Custom Fiberglass Parts

I never did any but from what I found on the net they are just plastic so drill slow and have some air blowing on them as you drill or they might melt. Made a couple of cheese presses for Melanie out of similar material and if we didn’t use compressed air the stuff would start melting real quick.

Steve

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Technology is great when it works,
and one big pain in the ass when it doesn't
Detroit iron rules all the rest are just toys.

Freeze it with nitrogen, then drill it while it's frozen.

quote Originally posted by Raydar: I need to enlarge the hole through a [urethane] control arm bushing to 13/16 ... What can I expect?

I haven't ever tried enlarging the holes in urethane suspension bushings, but here are some general "best practices" for machining soft plastic materials:

It depends somewhat on the original hole size. A standard drill bit will tend to grab in a soft plastic material like urethane, which is definitely not what you want. You can buy drill bits specifically ground for use on plastic (often labeled "acrylic" bits). If the original hole is only slightly smaller than 13/16 you might get best results with a chucking reamer. Whatever cutting tool you choose: 1) Use a drill press or vertical mill. You need precise control to keep the tool from grabbing. 2) Use a very slow cutting speed and a slow feed rate. This will both minimize grabbing and reduce the chance of melting the plastic. 3) Use a round holding fixture; a collet would be ideal. You want to keep the bushing perfectly round while drilling/reaming; otherwise your new hole will not be round. 4) Use a backing plate to prevent tearing as the tool exits the hole.

quote Originally posted by lateFormula: Freeze it ... then drill it while it's frozen.

A useful technique for some plastics, but you have to experiment. Liquid nitrogen may be too cold, rendering the plastic too brittle to machine, while simply chilling to 0 F in a home freezer may be sufficient.

[This message has been edited by Marvin McInnis (edited 08-16-2012).]

Marvin, you never cease to amaze me. You are a true gift to this forum.

Tony

Thanks, but I was simply reciting a hard-won lesson from the School of Hard Knocks. Ruining a $500 acrylic aircraft canopy tends to make one a true believer in learning the proper techniques for machining plastic.

[This message has been edited by Marvin McInnis (edited 08-16-2012).]

Thanks to all for your responses. I'm reading and paying attention.

quote Originally posted by Marvin McInnis: ...If the original hole is only slightly smaller than 13/16 you might get best results with a chucking reamer. Whatever cutting tool you choose: 1) Use a drill press or vertical mill. You need precise control to keep the tool from grabbing. 2) Use a very slow cutting speed and a slow feed rate. This will both minimize grabbing and reduce the chance of melting the plastic. 3) Use a round holding fixture; a collet would be ideal. You want to keep the bushing perfectly round while drilling/reaming; otherwise your new hole will not be round. 4) Use a backing plate to prevent tearing as the tool exits the hole.

This is exactly the case. What I have are typical Prothane bushings, with typical center sleeves, in a replacement set of upper control arms.
The problem is that the control arms do not have any "outside" support flanges on the frame. The original center sleeves in the rubber bushings have a flat flange on the "frame" side that is used to stabilize the sleeve. A bolt goes through the sleeve from the outside, and into a threaded insert in the shock tower. The flat flange on the inside edge of the sleeve is held against the shock tower. It's sort of hard to describe.

The new arms/bushings use the same bolt, through a huge thick flat washer, through the center sleeve, and into the shock tower. I have a concern that the replacement sleeves do not have the wide base/flange to stabilize them, where they contact the shock tower.

I'm wanting to drill the Prothane bushings and insert my original sleeves that I have already removed from my old control arms.
This may be overkill. They might be quite stable as designed. Just looks kind of "iffy" to me.

Raydar,
I lifted some info that may prove helpful from the Prothane website:

"Some of the '88 Fiero G.T. cars use a 1-1/8" diameter front sway bar.
Unfortunately, neither Energy Suspension nor Prothane will make a small bracket sway bar frame bushing in the 1-1/8" size.
Because the bushing would have an extremely thin side wall, The only sway bar frame bushings that will work on this application is modified small bracket design #9-5129-G (1.00").

YOU will have to place this bushing and bracket in a drill press vise and drill press to drill out the 1.00" hole to 1-1/8".
You must be very careful to center the drill bit to the 1.00" hole in the bushing.

Because the side walls will be very thin, it is easy to end up with a hole in the side of the bushing.
I have successfully drilled out some of these correctly, and I have ruined a few bushings, so be careful.

NO NOT use a fluted bit that you would normally use to drill metal.
Use a flat bladed wood boring bit.

You could also us a large round bastard file to enlarge the hole if you want too."


Also with regards to freezing the urethane so that it will machine easier, you could bring it down to -50F using Dry Ice.

I hope the info proves helpful.

~ Bob ~

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"Its nice to be important.
Its more important to be nice."

quote Originally posted by FieroBobo: Raydar, I lifted some info that may prove helpful from the Prothane website: "Some of the '88 Fiero G.T. cars use a 1-1/8" diameter front sway bar. Unfortunately, neither Energy Suspension nor Prothane will make a small bracket sway bar frame bushing in the 1-1/8" size. Because the bushing would have an extremely thin side wall, The only sway bar frame bushings that will work on this application is modified small bracket design #9-5129-G (1.00").

That may be the case today, but has not always been the case. Many years ago (17-19 years) I replaced my sway bar bushings, both the bushings and end links on my 88 with Energy Suspension parts. I used their "all purpose" bushings/end links that were the correct size for the front and rear on my car. I would be suprised if those bushings and end links were not still available, as they were not made for any specific vehicle.

[This message has been edited by lateFormula (edited 08-17-2012).]