Since joining TechShop I have been learning about machining on the vertical mill. One of the biggest challenges for me has been figuring out how to clamp work that doesn't fit easily in to the vice. While perusing "Practical Ideas... for Metalworking Operations, Tooling, and Maintenance, McGraw-Hill, 1984", I found an interesting idea that would help quickly align work right on the mill table using the T-slots.
The stop uses the squared wall of the T-slot to align the machined face of the stop, which is then clamped in to place with bolts in the stop itself.
It is easy to make and gave me some experience working with stainless steel.
I made it at TechShop
Step 1: Get Some Bar Stock
I bought some 1 1/2" wide stainless steel bar from the local metal surplus yard. It was about 5/8" thick which turns out to be a problem later. I cut a length on the cold saw to just over 12" long.
Step 2: Square Everything
I then squared all four sides with an end mill. Since I was planning to use the flat machined face to align with the T slot, I machined both faces as well. The 5/8" thickness was too much to fit in the T-slot with the bolt heads as well so I had to take several face cuts to thin the bar down to about 1/4". The bolts heads don't screw flush against the bar and I wanted a little play in the bolt too so I went back and thinned a little more. Some where between 3/16" and "1/4" worked well.
Step 3: Drill Baby Drill
Now, with a clean, flat piece, it was time to drill some holes. Starting with a 1/8" pilot hole, I worked up to the 5/16" bit called for by the tap for the 3/8" bolts.
After drilling, I used the mill to chamfer the holes. This put on a nice finish, but more importantly, helps to guide the bolts in to the holes. This is one of those finish things I never thought about when looking at parts but now I always see.
After tapping, I inserted all the bolts. I used 3/8"-16 steel bolts.
Step 4: Flatten and Shorten the Bolts
The bolts from ACE have markings on the tops that I wanted to remove to make the top flush, especially since there is limited clearance in the T-slot.
I ground the tops of the bolts on a disc grinder, using the bar as a holder.
I also cut the excess bolt off with a hacksaw so that I had just a few threads available. The bolt has to be long enough to have enough thread engaged to clamp but short enough that the bolt doesn't extend through the bar.
Step 5: How to Use
Once finished, the bar is inserted in to a T-slot. The bolts are tightened with an end wrench which causes the bar to clamp flush against the side of the T-slot. The head of the bolt presses against the other side of the T-slot to clamp the bar. If your T-slots are square, now you have a square edge against which to align a piece for face milling or other work.