Tool Post Holder

[BaronJ]

I am doing the boring on my lathe. Don't have a boring head for my mill/drill. I use a telescoping gage and a micrometer to measure the ID of the hole that I am boring. I am getting better at it. I now get consistent measurements. My measurements are smaller than the actual ID. How do I know this? As stated in a previous post my measurement of the ID of the hole is smaller than my measurement of the OD of the post yet the holder fits on the post. So the ID has to be bigger than my measurement.

Hi Mick,

Try doing it the old fashioned way with inside calipers and a micrometer.

 

[homebrewed]

Thanks, BaronJ.

I'll have to try a split clamp on the next tool holder I make. It really isn't much more work than what I did as shown above. I want to make a boring bar holder anyway....

 

[mickri]

On my first holder for my 1/2 & 5/8 boring bars due to a lack of room I used a 1/4 x 20 bolt as my clamping bolt. It only takes 1/4 turn to clamp the holder tight to the post. And it takes a lot of force on that 1/4 turn. On my next holder for my small boring bars I had more room for a larger 3/8 x 16 bolt. The force required is a faction of what was needed for the 1/4 x 20 bolt. Slightly less than a 1/4 turn to clamp the holder to the post. I now know that a 5/16 x 18 bolt will fit on the large boring bar holder. If I can figure out a way to fill the existing hole for the 1/4 x 20 bolt I will try to fit a 3/8 x 16 bolt on the large boring bar holder.
Moral of this is to use the largest bolt possible for the clamping bolt.

 

[homebrewed]

Moral of this is to use the largest bolt possible for the clamping bolt.

I would think the 20TPI threaded bolt has a greater mechanical advantage, so, all else being equal, it should be easier to tighten it down. Also, because of the finer thread, you would expect to turn it more for a given amount of "squish". I suspect you are mostly seeing differences between the two big holes you bored.

I used 10-24 bolts for everything on mine -- the closer and the 3 for holding the cutter in place -- and they work fine for me. However, my tool holders are made from 6061, not exactly an apples-apples comparison!

 

[BaronJ]

Hi Mick,

This is the way I measure a bore !


Outside spring calipers. If you buy a Chinese one, make sure that it has rounded ends, like small balls.
I've seen one that actually had tiny balls fastened on the ends of the legs.


This is how you use it. Here I'm going for 35 mm.


And here is the actual micrometer reading. Maybe 10 microns over.

 

[mickri]

Today I finished boring the last of the center holes. Next chore is to mill the slots for the atlas craftsman tool holders. I will measure the holders again. From memory they were 13/16 high by 3/8 wide. I am thinking of making the slot .82 high by .40 wide. The slot will be 2 1/4 long. Milling the entire slot would take me a long time. To make it go quicker I thought of drilling most of the material away and then cleaning up the slot with the mill. Which way to drill the holes is the quandary. And what size drill to use. I think using a 3/8 drill and drilling two holes the length of the slot would be better than drilling a bunch shallow holes.

Suggestions please.

 

[BaronJ]

Hi Mick,

I just clamped it up in the mill vice and ran the cutter across six times taking 2 mm deep cuts. But yes drill most of the meat out if it makes it easier.

Another picture for you,

Here I am about to take my third or fourth 2 mm cut. 12 mm four flute slot drill. Chinese HSS


This is one of my Norman tool post holders. It goes from free to locked with about 1/4 turn of the cap screw.

 

[homebrewed]

This is one of my Norman tool post holders. It goes from free to locked with about 1/4 turn of the cap screw.

Out of curiosity, how does your tool holder lock to the post? I don't see a slit cut in the holder, so the locking principle appears to be a little different from most Norman-style tool holders.

BTW I like the nut you made -- it looks pretty nice.

-H

 

[mickri]

Nice job on your tool holders. My boring bar holders are are a little on the rough side but work well. Mine also take only a 1/4 turn to go from free to locked. I have been using the two boring bar holders to bore the center holes on the remaining five holders. I have decided to complete one holder as a test run. I will try cutting the slot with just the end mill without drilling out most of the material to see how that works for me. I can hold all of the last four holders in my vise at one time.



That way I can cut the slot in two of the holders at the same time. Then do the other two. I have been using the slowest speed on my mill in previous projects. For this I think that I will figure out what speed I should be using and see how that works for me.

 

[BaronJ]

Hi Homebrewed,

It uses the original design of the Norman tool holder and is the same as Rolls Royce use in their experimental workshop.
If you scroll up the post you will see the drawings that I posted showing the split clamp. Posts 48 and 54.

The nut was a scrap of free machining 25 mm AF hex bar. Drilled and threaded 7/16" BSF.
The shaping was done with a carbide wood router bit.


The only reservation I have is that I only have 1/4" inch shank versions of these. I would have preferred a 1/2" shank one.
Run at around 800 rpm in the mill and about 600 rpm in the lathe.
This picture was when I did the Norman Tool Holder shaping on the back edges.


Here I am using the router cutter to round off a brass tip on the end of an M6 screw.