Basic Milling question, re-registering a hole after 180 degree rotation

WobblyHand

WobblyHand

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Trying to make a hammer, nothing too fancy. It has an aluminum handle and an 12L14 head. The head will have a brass and delrin tip. My plan is to use the mill to make the holes for the handle and a screw to fasten the handle to the head. I need three different diameter coaxial holes. A 1/2" hole for the shaft, a 0.25" hole for a screw, and a 0.375" hole for the counter-bore for the socket head cap screw. I just don't quite grasp how to reacquire the correct orientation after rotating the head 180 degrees for the last hole. The holes would look something like this crude sketch.

Hmm, end mills are short. One idea I had was to mill the 0.25" hole all the way through and use it as a reference for the third hole. That's not going to work! Seems my end mill has about a 3:1 ratio of length to diameter. I have a jobbers length 0.25" drill, but that doesn't feel precise enough to indicate on.

Also have a PFC-70 5C, but no tail stock for it. I think it has a 2.75" center bore height. Is it a bad idea to use this unsupported by a tail stock?

Is there a relatively simple way to do this? If not, what minimum stuff do I need? Guys, that was NOT opening the door to everything! Just trying to get going, and I'm finding it's tough, because some of the odds and ends you all have, just aren't in my shop yet. So, if you could give some guidance it would be greatly appreciated. Like, make this gizmo first. Using the gizmo allows you to make X and Y, etc.

I made the handle in my lathe. Knurled it with my bump knurler as an experiment. The knurling experiment did work, although it was clearly done by someone who barely had a grasp on the concept. The knurling made me want to get going again on the nicer knurler that @mikey has done.
 

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Seems like you could drill the 0.25” hole, then use an end mill for the 0.5” pocket (or bore). Flip the part and use a drill bit in the 0.25” hole to align it. Since you didn’t move the table, you should be able to keep the same side of the part against the fixed vise jaw and just tighten the vise while the drill bit is through the hole. Then you just need to make the counterbore with an end mill. If you had a counterbore bit, it would have a pilot for the existing 0.25” hole. The counterbore doesn’t have to be perfectly aligned so that seems good enough?
 
3 different hole sizes, 0.375, 0.25, then 0.5. I can mill two of them from the top. Say 0.375 and 0.25. But I can't figure out how to line up the 0.5" diameter hole to be coaxial with the other two.
 
jwmelvin said:
Seems like you could drill the 0.25” hole, then use an end mill for the 0.5” pocket (or bore). Flip the part and use a drill bit in the 0.25” hole to align it. Since you didn’t move the table, you should be able to keep the same side of the part against the fixed vise jaw and just tighten the vise while the drill bit is through the hole. Then you just need to make the counterbore with an end mill. If you had a counterbore bit, it would have a pilot for the existing 0.25” hole. The counterbore doesn’t have to be perfectly aligned so that seems good enough?
Click to expand...
I think that's a good option. Maybe I'll get a stubby drill for the 0.25". I've seen enough drill wander to not trust jobber length drills. As for the counterbore, it's a 1/4-20 SHCS, the head is 0.370, me thinks a 0.375 end mill is too tight. 7/16 might be better.
 
WobblyHand said:
I think that's a good option. Maybe I'll get a stubby drill for the 0.25". I've seen enough drill wander to not trust jobber length drills. As for the counterbore, it's a 1/4-20 SHCS, the head is 0.370, me thinks a 0.375 end mill is too tight. 7/16 might be better.
Click to expand...

For that matter, might as well make the 0.5” pocket first if you have a center-cutting end mill. Then the drill hole is shorter. I do like stub-length drills though.
 
I do have center-cutting end mills in 1/2". If I make the 1/2" diameter pocket, then I have to use a center drill to locate the 1/4" drill?
 
It is most important to have the .500 hole on center and accurate as that is what will align the head with the handle.
I would start by drilling about half way thru with a drill maller than the .25. I would then bore the .500 hole to size. This is where you may have an issue. The handle needs to be a light press fit into the head or it will wobble no mater how tight the screw is. From pounding most any glue will let go. So you need to either bore the .500 hole to fit the shaft or even make the hole a few thou to small and then turn the handle to fit the hole you made.
That was the hard part.

NOw for the matching holes from the other side make a fixture in the lathe that is a perfect fit into the .500 hole on one end and the other end just a bit smaller that the diameter of the head, with the big end faced off nice and square. Stick this into the .500 hole and bottom it out on the bottom of the vice. this will hold the head and its hole nice and square in the vice. Now drill and C'bore the .25 hole and .375 c'bore.

You are correct, even though the spec says the head is .370 it is not likely to fit into a .375 c'bore. There is tolerance on that head diameter, and it is rare for the head to be perfectly concentric with the shank. Per the engineering specs the recomended sizes for a 1/4 SHCS are for close fit .266 and for normal fit .281, the c'bore for the head is recomended to be .437.
 
WobblyHand said:
I do have center-cutting end mills in 1/2". If I make the 1/2" diameter pocket, then I have to use a center drill to locate the 1/4" drill?
Click to expand...

If you use the endmill first then yes you will need to use a center drill or spotting drill to locate the 1/4 drill.
 
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