# Boring a flat bottom hole



## Jonathans (Feb 15, 2015)

I need to bore a 1 27/64" diameter hole, 7/8" deep in a 1" thick piece of mild steel. I will then thread it 1.5-12tpi with a tap. I am guessing that I should bore to depth with an end mill.  What do I need to use after that to bring it to finished diameter and keep the bottom flat?
Does anyone have a suggestion as to how I keep such a large bottoming tap perpendicular to the work?
I'm working with a HF radial R8 mill.no rotary table.
Thanks


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## Andre (Feb 15, 2015)

The tool for this is called a boring head, it uses a single point cutting tool that's adjustable to bore different diameters of holes. Just like boring a hole in the lathe but backwards if you will.
Because of clearance on the tool, you won't get a perfectly flat bottom hole (there will be rings viable from previous cuts) so it will be flat with ridges in the bottom. To get a perfectly flat bottomed hole you'd need a boring and facing head. Which is out of most of our price ranges.


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## RJSakowski (Feb 15, 2015)

For true tapping holes, I use a spring loaded guide with a 60 degree point which rests in the countersink in the tap or tap wrench.  After boring the hole, do not change your table position or, if you have to move it, note the position.  When you are ready to tap the guide will maintain true alignment with the hole.  They are available from Enco (http://www.use-enco.com/CGI/INSRIT?PMAKA=325-5179&PMPXNO=5810267&PARTPG=INLMK3) for less than $15.  You can also make your own; it's a nice little lathe project.  Another great benefit; the additional support virtually eliminates tap breakage.

Also run a taper tap first.  It cuts much easier and there is less chance of runout.  Cut the last few threads with your bottoming tap to finish the hole.


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## davidh (Feb 15, 2015)

can a guy with average size arm power actually tap a hole that big by hand with accuracy ?


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## Jonathans (Feb 15, 2015)

Thanks. I'll look into getting a boring bar for the mill. I'll try the tap guide method. Do you think it possible to drill the tap shank to insert a 1/2" rod for mounting in the mill chuck, or will it be too hard?
I also thought it a good idea to run a standard tap prior to the bottoming tap, but at 1.5" these baby's get spendy!
The plate I'm boring and threading goes onto my forging press. I could through bore it and forget the blind hole altogether, but then my problem becomes how to tighten the plate to the hyd rod.  The plate is 1" thick 6x6". No way to use a setscrew


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## darkzero (Feb 15, 2015)

If you have access to a lathe & can mount the part, this job would be much easier in a lathe, for the boring & to single point the thread.



Jonathans said:


> I'll look into getting a boring bar for the mill.



Note, simply getting a boring bar won't work in a mill. You will need a boring head & preferable a facing head if you want to face the bore nicely. As Andre stated, facing heads are not cheap. They're similar to boring heads but I don't think there are inexpensive Asian clones for facing heads.

Doesn't sound like you really need to face the bore nicely. Just bore & tap.


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## dracozny (Feb 15, 2015)

darkzero said:


> Note, simply getting a boring bar won't work in a mill. You will need a boring head & preferable a facing head if you want to face the bore nicely. As Andre stated, facing heads are not cheap. They're similar to boring heads but I don't think there are inexpensive Asian clones for facing heads.



Facing can get a tad more complicated depending on what you want/need wohlhaupter probably makes the sweetest facing/boring head I have ever seen. with that said most probably don't need to do anything that would require such a tool. All of my facing needs are accomplished with a facing mill and those can be found fairly affordably.



Jonathans said:


> The plate I'm boring and threading goes onto my forging press. I could through bore it and forget the blind hole altogether, but then my problem becomes how to tighten the plate to the hyd rod. The plate is 1" thick 6x6". No way to use a setscrew


 I suppose my imagination is not working well for me at the moment. is the plate being used as a jaw on the press? is the bolt securing it from the other side or are you securing it from the working side?

as for the blind boring this style of boring bar I find more suitable for the job. 
	

		
			
		

		
	



Alternatively you could make something like this instead


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## darkzero (Feb 15, 2015)

dracozny said:


> Facing can get a tad more complicated depending on what you want/need wohlhaupter probably makes the sweetest facing/boring head I have ever seen. with that said most probably don't need to do anything that would require such a tool. All of my facing needs are accomplished with a facing mill and those can be found fairly affordably.



Yup, I agree. I was talking in terms of facing the bore for the facing head. There may be other ways but I only see using a rotab for that on a manual mill as the alternative. I'd love to have a nice facing head but it's just that, I don't need one, & would probably rarely use it anyway. I have a 2" Criterion & a 3" Yuasa boring heads so I'm good. I use a facemill & fly cutters for facing on the mill.


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## Chiptosser (Feb 22, 2015)

Can you weld the shaft to the plate?
If so, I would open the hole through the plate, tap then weld.


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## fgduncan (Feb 22, 2015)

If you are worried about locking the plate to the threaded shaft, you can do this. Bore through the plate and tap.  Put the shaft in with thread lock.  Then drill a hole into the face of the (now) unit right at the intersection of the shaft and plate for say a 1/4-20 bolt.  Thread the hole and insert a 1/4-20 bolt with threadlock. If you don't think one bolt will hold put a couple more. You have to shear the length of the screw before you break it loose!


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## epanzella (Feb 22, 2015)

Jonathans said:


> Thanks. I'll look into getting a boring bar for the mill. I'll try the tap guide method. Do you think it possible to drill the tap shank to insert a 1/2" rod for mounting in the mill chuck, or will it be too hard?
> I also thought it a good idea to run a standard tap prior to the bottoming tap, but at 1.5" these baby's get spendy!
> The plate I'm boring and threading goes onto my forging press. I could through bore it and forget the blind hole altogether, but then my problem becomes how to tighten the plate to the hyd rod.  The plate is 1" thick 6x6". No way to use a setscrew


Maybe I'm reading this wrong but is the only reason for the blind hole to jam the thread at the bottom of the bore to hold the rod tight? If that's the case, turn a shoulder on the shaft to tighten against and thread the hole right thru but one size smaller.


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## chips&more (Feb 22, 2015)

I’m agreeing with davidh. That’s a BIG tap! It will take different methods to get the job done. A little spring pointy thing for tap alignment ain’t gonna hold up IMHO. I think you will need a dead center type arrangement nested as close to the quill as possible and then feed the quill as you tap. As for the flat bottom hole. You can set-up a boring head to stop at a preset depth. So as you feed out for the next cut you continue to stop at that preset depth. The finish at the bottom will look kinna phonography but maybe that’s OK?…Good Luck, Dave.


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## Jonathans (Feb 26, 2015)

Well, this is what I decided to do after so many great suggestions.  I will through bore the plate and run the tap all the way through the hole.  I'll run some rod from the corners corners of he plate/die holder that will be guided against some uhmw on the supports of the press.  This will prevent any twist at all under high pressure, and provide me with good working room.
I'm going to attempt to hand tap the threads with the 1.5" 12 TPI tap I picked up using a guide on the mill.  I'll have a friend keep pressure on the tap while I turn it.


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## Fabrickator (Feb 27, 2015)

Why not do it in the lathe with a four-jaw chuck and boring tool.  You could also cut the threads instead of tapping them.  I didn't read it all, so I may have missed something.  But I just don't like hand tapping that big of a tap.


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## Cactus Farmer (Feb 27, 2015)

If you can hand tapa 1 1/2 hole, the arm wresteling match is off........................


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## Jonathans (Feb 22, 2016)

I thought I'd do a follow up on this string.
I did hand tap the 1-1/2 12 nf in my 1" plate.
The key was to position the plate and the no move it in the x or y axis until all the process was complete.
I drilled it out progressively to 1-13/64 and then used a Criterion boring tool to bring it right to 1-27/64.
I then mounted a dead center I made in a collet on the mill.  There was a factory hole in the top of the tap
And the dead center kept it aligned while I turned the tap with a twisting wrench I had made up from an
Antique wrench.  Keeping light pressure on the tap and turning it a quarter turn at a time did the trick.

Needless to say, I decided to abandon the blind hole concept.


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## FOMOGO (Feb 22, 2016)

looks like you "Got'er done". Many ways to skin that cat. Loving the double handled monkey wrench. Mike


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## kvt (Feb 22, 2016)

It looks good,   Now let us see it in action on that forging press you mentioned.


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## Tony Wells (Feb 23, 2016)

1 1/2-12 shouldn't be too bad, with the right wrench. I have done some 1 3/4-5 that was downright hostile though. I don't relish having to do any more of them now, especially with a damaged back.

I probably would have just made a jam nut for it to lock it in place.


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## Jonathans (Mar 6, 2016)

Well, at long last I got her done.  I think The next dies I make will be thicker to allow for greater visibility.
These should do the trick for setting a weld on a Damascus stack and drawing it out.

Here's the press next to its brother





View of the 1.5" tapped hole threaded onto the ram shaft.  It's on tight to the shoulder and secured from unthreading with a set screw.


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