Axle datum

[glh101282]

I have new axles on order through Colin Hyde. I understand about making the axle opening 1/4" wider front and back, 1/2" overall. Do I also need to remove 1/4" from the top of the opening? I have the standard 1" ride height.
Also, I have been told that new/modified holes will need to be drilled to line the axle mounting holes up with those on the trailer. I did not scribe the axle location as suggested in another post.
Is there one hole front or back that I can use as a datum? Even if the axle lines up a little further forward or aft, as long as the mounting hole used/datum for each side is the same they should be square with the trailer.
To compensate, I may have to take more off of the front/back of the axle opening to allow the axle to clear the frame. The axles may sit slightly (1/2" or less) further forward/aft than the original axles.
Am I off base with this thinking?

[dbj216]

Hello from Colorado: Sounds like you ordered the "series 11" Dexter axle with weight ratings from 3600# on up, 3" tube, and 12" brakes. I put one on the single axle 69 Globe Trotter that was 4500# rated.

Dexter has a drawing on their website showing the dimensions of the axle mounting brackets in relation to the tube. If I squint with my reading glasses on I believe the datum is the front surface of the tube. It seems like the mounting holes are dimensioned from this surface. Of course the axle bracket sits tight on the frame rail. The bolt holes just hold the axle to the trailer in case you fly off a cliff.

I've had to remove material from the axle plate (or Dexter mounting slots) on every one of the 7 new axles I've installed. Airstream axle mounting plates don't necessarily fit the Dexter mounting brackets. It is a hard job with a hand held 1/2" drill. The new fangled step drill bits work better. Or I get my little die grinder out and make a "key hole" in the axle plate so it will reach the Dexter slot.

I make a template of the Dexter mounting bracket showing the location of the Dexter mounting "slots". It helps my thinking and visualization of what had to be done to get the axle to fit up. I also made lifting aids to help a grandpa install the axles working by himself. I can't bench press a 200 pound axle into position.

Photos for fun:

David

[glh101282]

Thanks for the reply, David.

Good idea with the template. It looks like the aft mounting hole only needs about 1/4" out of it to line up the axle bracket with the AS support. I was thinking of using this hole as the datum and not doing anything to it, then cutting out the axle shaft opening and forward hole to allow installation of the axle.

I have seen the axle support drawing on the Dexter website and remember them showing the axle housing surface as being the datum for the dimensions. I do not remember the tolerances but assume it to be 1/8" or less. This would mean that the attachment hole may be off by that much in relation to the shaft surface. i do not think this will amount to much when pulling the trailer.

Again, is my thinking about using the mounting hole as the datum on the right track. I think I read somewhere in the forum that they used the aft hole as the datum/reference point. I am an engineer and may be over thinking the issue.

[glh101282]

Further update.

I found the axle mounting plate drawing and it looks like Dexter uses the centerline of the axle shaft as the datum for its dimensions. They also violate good drawing practice by not using the datum as the beginning point for all dimensions. This allows for tolerance stack up, except there are no tolerances given.

It makes me believe that tolerances are not important and my original thinking about 1/8" or less may be true for aligning the axles and trailer.

I can use this information to come up with a template to give me an idea of metal that needs to be removed, both lining up an existing mounting hole in the frame and using the axle centerline as a datum. End objective is to minimize the amount of metal that needs to be drilled/ground/cut from the AS structure.

[dbj216]

Don't laugh. I used a 22ga solid wire to measure the distance from the front of the ball coupler on the trailer to the center of the spindle shafts on both sides of the axle. The wire won't stretch or sag much. At least it gave me an idea if the axle was square to the axis of the trailer.

You are right. The mounting brackets are not precision parts. The Dexter drawing I down loaded didn't show any dimensions from the centerline of the axle. But drawings change.

Good luck with your project. It may be that your 1980 trailer has vertical bolts into the frame rail. I've seen this on other 1980's trailers, like my wife's 86 Limited 34'.

David