Boring a flat bottom hole

[Jonathans]

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

 

[Andre]

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.

 

[RJSakowski]

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.

 

[davidh]

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

 

[Jonathans]

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

 

[darkzero]

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.

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.

 

[dracozny]

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.

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

 

[darkzero]

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.

 

[Chiptosser]

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

 

[fgduncan]

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!