By Alan Lewis

 

I NEED D-SHAPED BUMPER STRIPS, BUT ALL I HAVE IS O-RINGS!

The game originally had D-shaped bumper strips along both sides of the playfield. They were 3/8" wide X 3/16" tall half rounds.

The first question was what rubber was used for this D-strip? It was white for sure but at 60 years old is was crusty and mushy.

Click on the above image to see the FTIR analysis of the original 60 year old rubber compared to a new white rubber pinball o-ring.

From this analysis plus a "burn" test on the old and new rubber I determined that the original ring was made from the same rubber as a typical new pinball rebound o-ring. In addition I determined that these o-rings are most likely SBR rubber approximately 50 durometer.

OK, so you are saying "what else is new, this FTIR stuff is old hat to the pinball restorer". To what length will a budget minded pinball restorer go to work around a challenge? I had some of the new large size white pinball o-rings hanging around so I figured that since they were the right rubber material I need to use them.

I had to cut an o-ring in half along its' length! Slice the round cross section into two D shaped cross sections.

A skiving die was made out of wood and an X-Acto blade.

A standard o-ring is cut in one place so it is straight. The end is hand split in half for about an inch so it can go through the die. Soap is used as a lubricant.

Once threaded through the die the rubber is pulled all the way through producing two D shaped strips.

That's all there is to it! (OK, so I am leaving out all the hard parts, nothing is ever that easy!)

The old vs. the new D-Strip.

The new one is smaller but will look and work just like the original. Same shape, same rubber.

Installed

This tool will save you a lot of headaches when fastening the rubber strips to the side rails. It is a Brad Setter and only costs $10.

The brad is held by a magnet and is gently pulled into the rubber and wood. No muss, no fuss!

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Copyright 2007 by Alan Lewis

No copying without written permission from Alan Lewis