setting up on a center mark

[quality junk]

I'm finally parting with some of my hard-earned to tool up for a job with my BP mill. I need to bore 33/64" holes in 3/4" steel plate on a center punch mark and have them wind up on the mark. I'm planning to put a drill chuck in the BP as it runs a lot truer than my old drill press, then use a small pilot drill followed by size and counterbore.

Question: What is the best way to locate on a punch mark? The bolt pattern is mostly circular with some variations and I can't get a blueprint anyway. The tool catalogue shows center finders and wobblers. How are they used? Is this the right equipment for the task?

Question 2: I need to counter bore the bolt heads down to flush. Is a 1-1/8" end mill OK for this, one that is good for plunging? After I locate on the center, should I counter bore after drilling or before? Piloted counterbore tools are horendously expensive and they didn't have much of a selection.

Advice is much appreciated and I thank you in advance for any that is offered.

QJ

[GWIZ]

Here's a small write up on wiggler.
http://www.shopfloortalk.com/forums/...9&postcount=25



Its best to first drill thru before you counter bore ( don't drill into the table).

I use end mills all the time for counter boring bolt holes.
Cut your speed at least 50% from that of drilling.
**Make sure the part is bolted down.
Use a 4 flute end mill, some end mills don't have full width cutting lips so check the cutting end before you plunge.
Use alot of cutting oil.

BTW, End-mills are not 100% flat on the end.

[Dave Lee]

I know what you mean GWIZ, about top quality wigglers being junk. I used a Starrett that belonged to a fellow machinist. It was great! So, I went and got one of my own. Between the time they made his and the time they made mine, they changed the design. His had a nice spring action to it as you pecked at the punch mark. The spring action wasn't there in my new one.

I normally, use a double ended edge finder. The kind with the pointed end. http://catalog.starrett.com/catalog/...s/1000/962.jpg You can line up the punch mark close, then advance the quill so that, the point enters the punch mark. Without moving the quill, adjust X and Y to line up the tip of the edge finder with the body. You can do this with the machine off. When you've got it aligned, retract the quill, turn the machine on and "peck" at the punch mark to see if there's any lateral movement of the tip and adjust if necessary. It takes longer to explain than to actually do it.

One word of caution, you can do the operation completely, with the spindle turning but, put a drop of oil in the punch mark or you just may unscrew the tip from the rest of the tool. Ask me how I know.


Dave

[GWIZ]

I would never intentionally touch the part with a wiggler.
If you damage the point its game over.

Actually you can get alot closer with a wiggler by sighting scribed lines then trying to pick up a center punch mark.
Center punching has a tendency of moving off if you don't hit the punch just right.
Assuming we're not talking about a center punch with cross hairs.

Originally Posted by Dave Lee

I normally, use a double ended edge finder

I only like the single ended edge finders. collets and drill chucks don't always clamp down on the shank properly on the double end ones.
Some ends on the double ended ones are too long to fit into a drill chuck.

[Dave Lee]

Yes, I would much rather use the scribed lines as a guide to simpy, verify, visually, that I've read the dials or the DRO correctly.

With the wiggler, I guess it's all in how one was taught. All of the toolmakers that I've worked with over the years, would "peck" at the center punch marks to locate the center, if center punching was done to the work piece
I do agree though, about sighting over scribed lines, being more accurate. When I'm working on a drill press and need those center punch marks to get the drill started, I keep a very pointy scriber, just for the purpose of pushing into the scribed lines, to make a preliminary mark. Then, it's easier to get the center punch situated and has less tendency to wander when struck.

As long as we're talking about wigglers here, a bit of caution is helpful for those, new to this device. NEVER, NEVER, NEVER, use your fingers to push the shaft to true it, while it's spinning. Use a block of wood, a screwdriver handle, the handle of your chip brush but, not your fingers. Push it a little too far and the shaft starts wobbling wildly and turns into a helicopter. The blood all over the Bridgeport, will tell you just how sharp that point is! It will happen in the blink of an eye.


Dave

[moe1942]

If you know where to put the punch mark then work off the edge. Need an edge finder but the graduated hand wheel dial is more accurate than whatever method you are using to locate the punch mark. I can't be more specific because there are too many unknowns in this equation.

I don't/didn't use a punch mark to locate precision holes. If this isn't precision work then just touch on the punch mark with a center drill. Close enough for government work.


Also all chucks are not created equal. Whatever is use as a tool holder should match the degree of accuracy required of the end product.

[MXtras]

All info above is sound and good advise, but I agree with Moe.

I would locate the center of the pattern and then work the math and use the dials to reach each hole. Or locate the first hole in the group and use the dials/DRO from there, compensating for backlash - using dial indicators if your really worried about it.

Your eyesight can get you inside the standard drilled hole tolerances and we are talking drilled holes here. Drilled holes should not require absolute precision - that's for bored holes.

You can spot an inexperienced designer when he tolerances a drilled hole to an overly tight location tolerance. That drives me nuts!

Scott

[USMCPOP]

A little info on wigglers:

http://www.littlemachineshop.com/reference/wiggler.php

http://www.metalwebnews.com/howto/wiggler/wiggler.html

[quality junk]

I should perhaps have described the problem more completely. I am adapting a SAE bellhousing/PTO to a Cat tractor engine. I have been unable, with my admittedly humble research efforts, to aquire a blueprint of the Cat flywheel housing, so measurment is pretty much out.

I have a source of transfer punch bolts. I'll drill and ream the two alignment dowell holes, then use the transfer bolts to mark the bolt holes and drill +1/64" holes. It's about the best I can do under the circumstances, but I am limited to the use of punch marks.

I gather from the advice given that I should keep the punch mark small, use a center point, then a spotting drill and eyeball as close as the old bloodshot eyes can get. Right?

QJ

[MXtras]

I would think that for a drilled hole this will get you close enough. Your eye should get you within .005".

Scott