Topic: Precise holes in square material

[70CB750]

When I need precise hole in anything rotational, the lathe is the best approach, I can even hold some squarish things in the lathe and cut a hole that is more accurate than drill press.

But when the lathe does not work, the drill press will not help.  Say I need a 20.8 hole in  6mm thick metal, how would you approach it?

I don't have a milling machine and substitute drill press for one does not work - it is not stiff enough for that kind of work.

Ideas?

[Cqyqte]

Four (4) jaw chuck and lathe is the only way I know of my friend.

[Steve_K]

20.8 mm? that's about 3/4 of an inch.  Most small drill presses don't have a chuck that large.  I use a Bridgeport mill at work and I would drill it undersize and then ream or bore it to size.  If you have a lathe and a face plate and the part is not too long to turn in the lathe you can bolt it to the face plate and then drill and bore it.  A precise hole should also mean being perpendicular to the surface.  Also if you want them exact distance apart a mill would be best or easier.
That doesn't help does it?  How about a hole saw?  The hole may not be exact, but maybe by making the mating part to fit hole might work.  Another way, use a larger hole saw and then make a bushing on your lathe to press in the square material.
I could think of other ways if I know what tooling you have.
Steve

[rhinoracer]

I've done a few by pressing a square shape into a round hole and also by using all sorts of files, but if you're looking for a machine shop finish you can look for a shop with a wire edm. (The finished corner will still have a filleted radius the size of the wire though).

[754]

Try a circle cutter if its a round hole . On your lathe, try to mount an angle plate or tombstone on the crosslide, there is kits for extended table.. 1080 has one on his Atlas.

 Boring head is a must have..

[scottly]

I have a 1" thick plate bolted to my faceplate, with different bolt patterns drilled and tapped. This is what I used to make spacer/centering rings to mount Yamaha discs to my front hub.

[754]

 You have to think outa thebox, I use a small 4 jaw in my 3 jaw a lot, in this case turning fuel ine spigots onto a custom fitting.. The spigots are 8 mm.

[Steve_K]

The above posts have good ideas.  Like 754 says think outside the box.  There always more than one way to do something in a machine shop.  I have been down that road many times.  Most machinists are always looking for different ways to do things. 
Lindsay Publicans had a website with old time machinist books.  I believe he has retired, but there is likely other sites.  He had some great books.
Steve

[754]

 Might be easier to post a drawing and for us to make it.. Take less time than talking about it..lol..

[XLerate]

When I need precise hole in anything rotational, the lathe is the best approach, I can even hold some squarish things in the lathe and cut a hole that is more accurate than drill press.

But when the lathe does not work, the drill press will not help.  Say I need a 20.8 hole in  6mm thick metal, how would you approach it?

I don't have a milling machine and substitute drill press for one does not work - it is not stiff enough for that kind of work.

Ideas?

I'm no machinist, not even close, just a lifelong mechanic and fabricator. The following isn't meant as attack or insult, just as information gathering, so please don't be offended if it sounds mean or something.

What do you mean by precise? Is that +/- .01", or .001", or .0001" or .00001"?

Why won't the lathe work, as in what's the particular limiting factor? Overall size or shape of piece to be drilled?

What do you mean by 'metal'? Aluminum, Titanium, Berrylium, Iron, Cobalt, Tungsten, Steel, Magnesium? Makes a big difference in how to answer.

Is it a one-off piece? What sort of function is it supposed to serve or what is the piece or part's purpose or use? What is its value? If it's worth $78,000 you might want to use different methods than if it's worth $0.78.

Can you not pilot drill and ream to size? If not, why not?

Does this situation occur often enough and with enough importance that an investment in tooling is valid? With more precise information provided others, probably not me, can give more accurate advice.

[crazypj]

Remove tool post and  compound slide and bolt 'whatever' on cross slide
Hold bit in lathe chuck
It's possible (but not recommended) to either use spacers and/or offset jaws by installing them 'wrong' - out of sequence (in a 3 jaw self centering chuck)
You can also offset tooling by using 1 or 2 reverse jaws, spacers and sequencing.
 I opened up the crankcase mouth on CJ250 to take GS1000 liners using these methods (14mm overbore  )
If you have a 4 jaw chuck, offsetting is real easy

[FrankenFrankenstuff]

I like this riddle.

My lathe is a 3 chuck and when I have an odd shape to fit in.....I just make a collet to fit into the center. Typically I just center the item in a cylinder and pour plastic around it. When the plastic cures I remove the item and then band saw in a couple little flex/compression points (not all the way through) so the 3 jaw can really compress both the collet and the item inside the collet.....granted this is typically safe at low speeds and I am usually only either drilling or tapping a plastic.

Have you checked McMaster Carr?
http://www.mcmaster.com/#standard-square-washers/=liwkyi

[scottly]

Might be easier to post a drawing

1+ It's hard to think outside the box without knowing the size of the box. Just what are you trying to do?

[Doggie]

Like someone said, it might be better to just send a Machinist the part to do. I am a Prototype Machinist by trade and would make it for you. Just send me a drawing or sketch of what you want.
                                     Doug

[scottly]

I believe the OP does have machining skills, and this is more of a language issue since English is not his native language, although he often has a better handle on English than some native born Americans..

[70CB750]

Gentlemen, thank you for your time. 

I came up independently with Scottly solution, I took off the 3 jaw and found that I can get a piece of steel mounted on the lathe and use that as a face plate for whatever shape I have to fasten - drill and tap holes as needed. 

754 idea of 4 jaw in 3 jaw is quite original, I applaude.

As far as machining, I have more theoretical  education than skill - but I am learning


What I am trying to do is a lever to weld on the rear brake pedal to actuate the rear master cylinder - see the picture. 

[scottly]

What I am trying to do is a lever to weld on the rear brake pedal to actuate the rear master cylinder - see the picture.

Before you do any welding, please post a picture of the fabricated lever, showing where you are going to weld it to the brake pedal. It appears to me you would only want a half circle cut into the lever, not a full circle. You can only weld on one side of the split in the pedal, or you will not be able to tighten the pedal to the pivot shaft.

[754]

I had a hard to hold piece today, the outside width is about .24 and approx 1.85 dia the inside where I had to remove material had a counterbore, 1.75 od and 1.375 id , but only .095 thick.. That lip is what i had to turn down .So I held it on the 95 thou thick part, and then turned that counterbore (and holding material), down tob55 thou.

 Looked like this.....

[scottly]

OK, I give up. What is it?

[754]

Its for a downhill bicycle ..goes between sprockets and frame, keeps chain from jamming if it comes off.

[70CB750]

What I am trying to do is a lever to weld on the rear brake pedal to actuate the rear master cylinder - see the picture.

Before you do any welding, please post a picture of the fabricated lever, showing where you are going to weld it to the brake pedal. It appears to me you would only want a half circle cut into the lever, not a full circle. You can only weld on one side of the split in the pedal, or you will not be able to tighten the pedal to the pivot shaft.

Exactly!  I measured how much difference the bolt makes and it is quite a lot - I don't want a wobbly brake pedal even if it would be only from side to side.

To clarify what I mean by precise, 0.1mm is typical, with a bit of dedication I can get to 0.05mm but that's about it for the old Logan of mine.