Reference points for adhesive tape measures on Arctos-style jig

General Discussion
1

Hi everyone,

Can anyone tell me where the measurement tapes on an Arctos jig are zeroed? Specifically:

•	Rear axle vertical
•	Head tube vertical
•	Horizontal tape

I assume both verticals reference the bottom bracket centerline as zero, but I’m not sure where the horizontal zero point should be.

Thanks,
David

2

0,0 on my Arctos clone is the BB center. Everything is referenced off of there in X/Y coordinates.

I have scales glued on in some areas but it’s also pretty easy to use a high quality metal scale that you remove after measuring. You’ll never burn that one. If I were making my fixture again I would just make scale holders on each adjustment at the 0 point and remove the scales once set.

2 Likes
3

Thanks a lot for the quick reply Alex. That is a great idea about having removable scale holders. I am in the process of building my first jig now and this piece had been confusing me.

0,0 as the BB center makes sense. For the horizontal scale, do you just place the seat tube / BB holder at a particular horizontal location and call that zero?

Thanks,
David

4

On my fixture I made the main beam exactly horizontal and engraved a fixed distance on the ST angle bracket to the BB. This sets the virtual BB location in Y and it’s a fixed distance from the top of the main beam. So you can also make a scale for BB drop/rise based on knowing that relative point.

Photos of my fixture here:

I can’t read this engraving in the photo, but I think it says 8in:

image
image1034×1132 295 KB

5

I should add that I built this 15 years ago and it’s taken apart right now so some details are fuzzy.

6

For the horizontal scale I think I made the HTA lower cone centered at zero, so BB would slide away from zero to the X,Y datum.

7

Thanks again Alex. I think I understand what you’ve done here and am impressed you remember so long after the fact!

Cheers,
David