How would you drill holes in the end of a long plate?

[bpimm]

I need to drill and tap 3 holes in the end of a 4" X .5" plate that is 14" long to match another part that mounts with 10-32 screws. This is part of the new Z axis I'm building for my plasma table.

I was thinking of making a drill guide out of mild steel on the cnc to get the spacing right and clamp it on the end then hand drill.

Any better ideas? here is the part the holes mount the plate the motor is on to the vertical plate that is blue.

Thanks for any advise
Brian

 

[chips&more]

What tools -machines do you have to do the job?

 

[Bob Korves]

If you have access to a milling machine with a turret to drill with, I would clamp and square the work to the side of the table, and then swing the ram for clearing the knee with the work.

 

[brino]

Whatever you use to get the first hole aligned, I would finish tapping the first hole and bolt it before moving to drill the next hole and continue in this manner. That is, use the final fasteners as the "clamp" to keep the pieces aligned as you go along. I have had much better alignment when following this practice.
-brino

 

[RJSakowski]

I take it that your motor mounting plate is already made. Typically, I would use the technique used by medieval locksmiths who made the lock to fit the key. I would drill and tap one hole and mount the motor plate to use it as a template for the second mounting hole. If your other holes are already made, I would do the complete assembly up to get my alignment as close as possible. I would clamp the assembly as well as I could and then drill and tap the first hole. Then I would bolt that hole up to further define the alignment and drill and tap the second hole.

Of course, having a CNC, you can make a jig to accomplish the same thing. A little more work up front but easier and potentially better results on the back end. As for the actual drilling and tapping, if you have a drill press with enough clearance, you can swing the table to the side and use Bob's clamping approach to drill and tap. Or you can make your jig an inch or so thick which should be sufficient to make the holes run true and use the hand drill.

 

[RJSakowski]

Whatever you use to get the first hole aligned, I would finish tapping the first hole and bolt it before moving to drill the next hole and continue in this manner. That is, use the final fasteners as the "clamp" to keep the pieces aligned as you go along. I have had much better alignment when following this practice.
-brino

Damn, Brino, you type faster than me!

 

[bpimm]

What tools -machines do you have to do the job?

I have 2 drill presses and 2 mills to work with besides the standard hand tools. See below.

If you have access to a milling machine with a turret to drill with, I would clamp and square the work to the side of the table, and then swing the ram for clearing the knee with the work.

Bob, if I'm understanding you correctly you are suggesting swinging the head so it is no longer above the knee and has access to the back edge of the table. I could do that on either mill. One is a round column benchtop Grizzly RF clone that has been converted to CNC, I'd have to remove the flood coolant containment box from the table on this one but it's really easy to swing the head and I already have the hole pattern programed for it.

Or I have a Jet Knee mill that could do that as well, needs a little cleaning.

This one can swing the head and I can use the DRO for the drill pattern so I guess either can do it so it boils down to which is easier to set up.

 

[bpimm]

I take it that your motor mounting plate is already made. Typically, I would use the technique used by medieval locksmiths who made the lock to fit the key. I would drill and tap one hole and mount the motor plate to use it as a template for the second mounting hole. If your other holes are already made, I would do the complete assembly up to get my alignment as close as possible. I would clamp the assembly as well as I could and then drill and tap the first hole. Then I would bolt that hole up to further define the alignment and drill and tap the second hole.

Of course, having a CNC, you can make a jig to accomplish the same thing. A little more work up front but easier and potentially better results on the back end. As for the actual drilling and tapping, if you have a drill press with enough clearance, you can swing the table to the side and use Bob's clamping approach to drill and tap. Or you can make your jig an inch or so thick which should be sufficient to make the holes run true and use the hand drill.

Yes the motor mount plate is done but the holes in it are clearance holes and wouldn't center the tap drill well, I could transfer punch it and drill but my accuracy that way would be suspect.
My floor standing drill press can swing and rotate the table to do this but both my drill presses are on the cheap side and kind of sloppy.

 

[bpimm]

Whatever you use to get the first hole aligned, I would finish tapping the first hole and bolt it before moving to drill the next hole and continue in this manner. That is, use the final fasteners as the "clamp" to keep the pieces aligned as you go along. I have had much better alignment when following this practice.
-brino

I have done this in the past definitely good practice.

 

[wawoodman]

You could make a plate to hold a hardened drill bushing, and clamp that to the workpiece.

For that matter, if it's just three holes, make a guide out of some 1/2" aluminum. That will hold your bit straight enough for the tapped holes.