For those that have done it, what is the easiest way to cut a hole in a 26-27 dash to install a speedometer? Is there an adjustable cutter that can be used in a hand drill. I have seen where people have marked their circle and then drilled a series of very small holes inside the circle. Then the holes were connected by using a saw blade. I want a good job, but there must be an easier way to do it other than drilling all those tiny holes.
Measure the outside diameter of the speedo to get the proper size hole. Than buy or borrow a round Greenlee radio chassis or sheet metal punch and die in that diameter. (check on ebay for used ones). Center punch the exact center where the speedo head must fit; drill a pilot hole for the bolt of the punch/die. install the die on one side--punch on other. Turn the bolt until the die punches a neat factory type hole through the panel. I presume you are using the 26-7 small Stewart head not one of the earlier large ones. (large Greenlee sets are pricey). Also put some grease on the bolt threads and under the bolt head (turns much easier).
Or you could just get a hole saw and use it in your drill. Probably cheaper too, although you will have to clean up the edges a little bit with a file or Dremal tool / die grinder.
I do find sometimes with a hole saw that getting the exact size is a little to big---due to the total runout in the saw/drill bit/drill. So say you need a 2 5/8" hole, it may be useful to get a 2 1/2" hole saw and gradually file or dremel the hole to size for a better fit. If you want a real good fit, drill a piece of scrap metal first with the saw you choose and see how it fits before permanently altering your T.
Here's what I did Sunday to switch from the dinky 160 to a 490 (I think):
First laid the speedometer rim where I wanted the hole. I used a metal scribe to mark the primer.
Then chain drilled using a 3/32" drill bit:
Used a 3/32" router bit to cut the extra metal away crudely:
Then used a 1" carbide rotary file to clean up right to the line:
Then mount the speedometer case without the mechanism so the hole for the trip reset can be located properly, and drill the mount bracket holes. Total about 1 hour in the 100 degree garage.
If your gas tank is in the cowl just be sure to locate it where the clearance to the tank will permit attaching the cable and be careful with the pilot drill if you use a hole cutter so you don't hit the tank.
490 is the smaller head, Royce - clean job !
Them airplane tools work just fine on Model T's.
Nice job Royce
The AC speedometer that I would be installing, is roughly the same size as a Stewart 160. Stewart 160's were offered even after the Stewart 490 was produced and even has a special mounting plate that is different from the mounting plate for pre 26 dash panels. The Greenlee tool is a new one to me. It probably wouldn't be economical to buy a large one of the proper size, unless somebody has one to loan. The car is a four door sedan so no gas tank is under the dash to worry about. I would like to locate the speedometer as close to the factory dash light as is practical.