Precise Frame Measurement

[OldSub]

I'm building a '55 1st GMC 1-ton to pull my car trailer.  Power will be a 500 Cadillac with a TH 400.  The rear is a 14-bolt full float.  Front suspension will be the IFS from a 70's Chevy 3/4-ton with disk brakes and power steering.

I've been thinking a lot about making precise measurements as I make modifications on my frame. Recently my brother showed me a $600 piece of bar stock that had a number of threaded holes in it. The holes are for mounting a caliper to the bar, to make the bar part of a long precise measuring tool.

So after looking at that I was thinking I could make something using the same idea but based on stuff I have laying around.

I have some 10 foot sticks of conduit leftover from a project a few years ago. So I was thinking I'd contrive a way to attach a caliper to one end, and drill a hole on the other to allow mounting a pin to measure from. As long as the caliper is mounted in a way that is stable, and the distance from the stationary point to the drilled hole is known, I should then be able to make accurate measurements of about ten feet without the problems associated with holding both ends of a tape measure and then reading it accurately.

Drilling more holes allows shortening the measurements. Splicing two pieces of conduit would allow extending the reach up to 20 feet.

Since most of my measuring points are holes drilled in the frame, I can use the lathe to turn rod to exactly fit those holes, and either turn some of the rod small enough to fit in the hole drilled in the end of the conduit, or drill a hole in the one piece of rod (on the lathe to ensure its centered) and drop a smaller rod to match the hole in the conduit into.

Does my description make sense? Is there a better way for a guy working alone to make precise measurements up to 20 feet? Is there a commercial product that does the same thing and doesn't cost more than a cheap caliper, a couple sticks of conduit (all of which I already have) and a little hardware?

[DrJ]

Sounds like a sound idea there.
But it's very exacting, and since most people work on a 1/8"± tolerance, maybe to the point of insane frustration.
I think I'd make one of the pins fit the frame hole exactly and turn a 1/8" step in the other end along with the exact size, just so you have a go/no go amount of gimmie built in.
Also, I find that twist due to welding on an area is a bigger problem than changing triangulation.
To check for this I stretch two lines, like carpenter's chalk lines, without the chalk, across the frame from points near the end that should be level and check that they just touch each other at the center. That way I know there isn't any twist.
(Again, with a 1/8" tolerance)

[enjenjo]

I'm thinking two pieces of conduit/tubing. one that slides into the other. a nut welded over a hole in the larger one so you could lock it in place with a bolt. Intall a pin in one end of each tube. Taper the pins on the end so they will center in multiple size holes. install a 1/4" stud in the end of one pin, so you could run a wing nut on it to hold it in place, while you checked the other end.

Or you can do what I do, make the wife hold the other end of the tape, and yell at her when it comes out wrong.

[wayne petty]

harbor freight has this magnetic measuring tape
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=66420 might be used end to end to make it like a giant tape measure on the tubes or on rectangular tubing...


a strong ring magnet.. a chunk of clear plastic.. glued together with a hole drilled on the center line...  and another one drilled from the centerline on the magnet side.. off to the outer edge of the plastic will allow it to feed a line with a plumb bob up and down... with the magnet holding the clear plastic chunk over the center of the alignment hole...  masking tape on the floor to mark the center...

this 8 buck 24 inch caliper might be put to use also...
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=96509

just a thought...

got any frame shops near by???   you might ask them if you could look at their frame measuring gauge.. to get some ideas...


here is one brands measuring tools...
with a video
http://www.staraliner.com/measurec.htm


one more thing..

there is a site of Ebay that sells frame dimension charts for like 5 bucks..

http://shop.ebay.com/items/_W0QQ_nkwZcadillacQ20frameQ20dimensionQ20chartsQQ_armrsZ1QQ_fromZR40QQ_mdoZ


oops.. i looked up cadillac... then i realized its a 55 gmc...

[OldSub]

I eat better if I avoid yelling at my wife.  Besides I get to spend more money in the shop if she is gone shopping when I'm playing.

That $8.00 24-inch caliper needs to be part of my plan.  I can see trimming the movable piece and clamping it in one end of the conduit, and using the rest as my measuring tool.

Thanks for that idea!

[papastoyss]

I'm thinking two pieces of conduit/tubing. one that slides into the other. a nut welded over a hole in the larger one so you could lock it in place with a bolt. Intall a pin in one end of each tube. Taper the pins on the end so they will center in multiple size holes. install a 1/4" stud in the end of one pin, so you could run a wing nut on it to hold it in place, while you checked the other end.

Or you can do what I do, make the wife hold the other end of the tape, and yell at her when it comes out wrong.

My daddy was a carpenter, he used to say "here boy, hold the dumb end of this tape measure"!

[Harry]

Put a magnet next to where you are measuring from. Put the end on the tape measure on the magnet. Walk to wherever you want......

[OldSub]

Put a magnet next to where you are measuring from. Put the end on the tape measure on the magnet. Walk to wherever you want......

Thanks Harry, I like that idea!