Like before, I made this at TechShop (www.techshop.ws).
Step 1: Parts and Equipment
The caliper is mostly made up of steel scraps that I had on-hand, but if you had to buy everything it’d probably cost about $20-25 from your local hardware depot.
1 in. x 1 in. x ⅛ in. steel angle, total of 12 linear inches
1 in. x ⅛ in. steel flat bar, total of 6 ½ linear inches
2 x #6-32 x 1” machine screws
4 x #6-32 nuts
1 magnet (I used a 40mm 15 lb pull round magnet from Harbor Freight, but anything similar would be fine)
You’ll need the following equipment:
- angle iron notcher
- drill press, 5/32 in. bit
- cold saw or vertical bandsaw
- Dremel tool with cutting disk
- hand file
Step 2: Construction Steps
To make the base pieces, you’ll want to end up with 2 lengths of the steel angle, each approximately 6 inches long, with most of one side notched out (but leave at least 1 inch). It’s easier to work with a longer length so, if possible, do the notching first and then cut to size. See the picture for what you should end up with. Remember that the base pieces are identical and not mirror-images of each other.
The notcher exerts a lot of force and may bend the base pieces. If this happens, just use some vise grips and bend things back. You may also want to clean up any sharp edges with a file and/or grinder.
For the uprights, you want two pieces of flat bar, each 3 ¼ in. long and 1 in. wide. You’ll then need to create a 1 ¼ in. x 5/32 in. slot in each. It takes several steps to create this slot:
- score a line down the centerline of each piece
- create marks on the centerline at ¼ in. and 1 ½ in. from the top edge
- drill 5/32 in. holes at both of these marks
- drill several more holes between the first two, spacing them pretty close together
- use a Dremel tool to cut away the material between the hole. (Make cuts along the tops of the drill holes and the bottoms. Flip the piece over and repeat. Then remove the material in between.)
- the drilling and Dremeling will leave the slot pretty rough so use a hand file to clean things up. This may sound like a lot of work but mild steel files easily.
Drilling into such small pieces of steel is difficult since the piece wants to “helicopter”, or spin around, putting you at risk for injury. To do this safely I built a simple jig with some scrap plywood to hold things in place. The jig also turned out to be useful for the Dremel step since I could clamp everything down.
Step 3: Assembly
Using two nuts, secure a bolt in each upright’s slot. Position the base pieces back-to-back and place the magnet at the base between the uprights; The magnet holds the base pieces together but still lets you slide them side-to-side to adjust the opening. The bolts can be adjusted up and down by loosening/tightening the nuts (hand-tight is fine, though wingnuts would be an improvement). There’s enough adjustment range to setup for both lateral and radial trueness.