All that glistens is not gold!

[Arnak]

Hi Folks,

So I decided to make a an in-line boring tool to bore out 2 bearing holes.

I made the bar and drilled the hole for the HSS tool bit, all OK so far.

After spending at least 20 minutes getting the bit to the correct angles and nice and sharp I put it into the bar and set the cut...

With the lathe running nicely and a small cut on I tried boring out the already drilled holes in the mild steel... bang, that was the tool bit breaking off.

So I took in out, resharpened it and tried again with the same result, not being one to give in easily I sharpened again and once more attempted to bore the holes.....

With the same result.

Obviously it was time for tea and a fag...

Back out into the workshop as I had decided to try another piece of tool steel in case I had overheated the first one in shaping it.

Then I had an idea:idea:

Why not check the old tip for hardness with a junior hacksaw blade...

The blade cut it easily.

Then I realised that it wasn't tool steel at all but probably a piece of key steel, whatever it was it was soft.

So I made a new tip from real tool steel and it cut the mild steel like butter.

Which just goes to prove that not all steel in the tool steel tin is actually tool steel!!!!

I must remember to test it first next time.....

Arnak

 

[Antman]

Hey Arnak
I keep some steel nails with my 4mm round HSS to practice grinding, especially bits to fit the boring bar at 45deg. I haven't tried line boring yet. Did you make some arrangement to advance the bit?
Ant

 

[Arnak]

Hi,

Ahhh, that's another story...

Do you ever get that feeling of.. I didn't mean to drill that large size straight through the boring bar?

So no I didn't but I did mean to add a grub screw to advance the bit.

I didn't worry about going for 45 degrees as it was going right through 2 holes, one behind the other.

Just a straight through hole was fine.

Arnak

 

[Lykle]

Another way to advance the bit is to use a center in the tail stock that you can move over.
For instance a boring head or something like that.

All you need to do is increase the diameter of the path that the tip is making, not necessarily move the tip in the rod.
By moving the tail end of the boring bar towards you, or away from you, you put the boring bar at an angle and that will increase the diameter of the tool tip.
And by using a boring bar or something adjustable with a screw, you can do it to quite high precision.

Lykle

 

[goldstar31]

Hi,

Ahhh, that's another story...

Do you ever get that feeling of.. I didn't mean to drill that large size straight through the boring bar?

So no I didn't but I did mean to add a grub screw to advance the bit.

I didn't worry about going for 45 degrees as it was going right through 2 holes, one behind the other.

Just a straight through hole was fine.

Arnak

There is a more elegant way. Years ago when I was making a Quorn tool and cutter grinder which involves drilling 3 precise 1.000" and a 1.003" bores, for bed bars 3.500" apart- and then split one ( per the book) I made up a pair of George Thomas boring bars which adopt 40 degrees to advance the cutters- precisely 0.001" per graduation of the adjuster.

Once it is done, it is done for ever. The only thing was not to split the rear casting but I digress. Then you have the tool which will make a staking etc pillar tool and so on. Only to do once:hDe:

I'll get me coat

 

[Arnak]

Hi Lykie,

Just a quick question regarding your suggestion for setting over the tailstock.

Wouldn't using the set over method produce a tapered hole especially where the 2 bearing holes are reasonably far apart?

Arnak

 

[goldstar31]

If you turn between centres you stand a chance of tapers. If you bore with a boring head, you will have a far better chance of parallelism.

I suggested a boring bar between centres to go through two castings and get 3.500" distance apart- and dead on bores sizes.

You can agree disagree or what you will. That was the way of the old masters and who am I to argue?

 

[Arnak]

Hi Goldstar,

I wouldn't dream of ignoring the old masters advice.

I may be wrong but I thought that Lykle mean using a between centres boring bar and setting the tail stock end over to increase the diameter that would be cut.

That I believed would cause the bar to cut on a taper or am I wrong.

I completely agree that a bar between centres is the way to go especially if your lathe is set to run completely parallel which in a good lathe it should automatically be.

A boring head is not an option for me as the holes will be too small to get the head through.

Arnak

 

[goldstar31]

Get 'Thomas' but even with an offset back centre, a boring bar between centres will bore parallel. It will be 'out' for measurement but if you haven't got a micrometer adjustment which is a micrometer adjustment and an 'iffy this an that' you simply have to faff bout measuriuing and cutting and measurement and cutting-- and then make a balls of it.

As for a boring head, Thomas bored to a quarter with his tooling. Sorry but he was one of the old masters and is still worth a read up.

I made a lot of GHT stuff, and have never regretted the time. I do regret the time that I also resorted to gimcrack tooling.

My views, and a lot of other people.

Norman

 

[Arnak]

Hi Goldstar,

Thanks for the timely reminder re G Thomas books.

I just realised that I had his workshop book in my library.:wall:

A quick look through revealed his boring bar methods, so I can have a go at making a suitable bar from his plans.

I still do not understand one point that was raised, I know understand how a boring bar will turn parallel as the work moves to the cutter not the cutter moving along the work as when making a taper.

What I am confused about is the idea of offsetting the tailstock to increase the cutters radius, surely taking that option the cutter radius is only increased in one plane, say the horizontal.

Would that not make an oval hole or am I once again missing the point of how it would work, perhaps you have to offset it in both planes, horizontal and vertical?

Arnak

 

[goldstar31]

Thomas goes through it but it is simply trigonmetry. Really, i would experiment with a bit of wood as the test piece. It would take too long in trig to explain here.
It certainly cannot be oval. If it is, you have just about entered the realms of ornamental turning with a 4 th dimension.
cheers

Norman

 

[romartin]

Maybe I'm tired (here in Rome it's bedtime), but my visual imagination tells me that offsetting the tailstock wont cause the boring bar to make a bigger hole; I think it will make the same sized hole but in an offset position of the workpiece. If you offset the tailstock so that the center of the orbit of the tool tip moves foreward by 1mm then the radius of the bored hole will not change but it's center will move foreward 1mm on the workpiece.
It also seems to me that, to a very small degree, the bored hole will be oval owing to the fact that the orbit of the tool tip is not perfectly square with the lathe axis.
In fact I think Lykle didn't suggest offsetting the tailstock; he suggested some device in the tailstock which would increase the diameter of the tool tip orbit without moving it's center.
And now to bed!

 

[goldstar31]

Ian if the tailstock is moved whilst the work is being machined, it will turn oval but this is the Fourth degree.
If things are static as in normal turning it will be round- a parallel boring.

A Greek guy called Euclid expounded the matter.

Good Night from the Roman Wall:wall:

 

[Arnak]

Hi Folks,

I've been working in the 4th dimension for a long time.

The 4th dimension is of course time.

Every job I do takes longer than I had planned it to be so there must be time slippage in the equation somewhere.

You must all know the feeling, you yell out to the wife, "I'll only be 5 minutes dear" then 45 minutes later you still haven't quite finished that job but you go in and your wife remarks, "Don't blame me if your dinner is cold as you said you'd only be 5 minutes!":hDe:

"What was that dear? OK I'll be right there, I'll only be a minute as I just want to finish this message"

I don't understand Euclid's theory's it's all Greek to me!

Arnak

 

[old-and-broken]

the hole that is bored by the offset tailstock will be circular in respect to its own axis.

If the hole has an axis that is not perpendicular to the entry or exit face it will describe an oval shape on that face when viewed along the axis followed by the hole.

The hole will in no way be an oval, it is an optical artifact.

 

[dsage]

romartin:

Don't be confused by the fact that the tool is inside the work. Moving the tool outward is no different than moving the tool inward when it's on the outside. The tip of the tool is a fixed point with respect to the central axis. When boring, the work is moving back and forth across the fixed tool tip.
Think about a tool mounted in a tool holder. If you rotate the compound around 30 degrees and use it to feed the tool on an angle. It still turns round parts when you move the tool across the part on the outside.

Sage

 

[goldstar31]

Isn't the answer to actually cut some test piece to see what happens in real conditions- and report?

N

 

[Lykle]

Hi Guys,

I used this method to build my over the top ball turner.
And no, you does not turn a taper, nor does it create an oval.

All you do is you move the tip of the cutting tool a little towards you, increasing the cutting diameter.

As you move the block of metal you are cutting back and forth with the carriage (which is supposed to be parallel to the axis of the lathe) you will cut a nice parallel hole.

Sure, you will also alter the angle of the cutter in reference to the material, but this angle is very small, so I chose to ignore it.

Lykle

 

[romartin]

Maybe I haven't understood the setup Arnak is using. However I will try to explain more clearly what I mean.

My earlier post was written in the belief that Arnak's setup has

• the boring bar, with it's tool bit, rotating between centers,
• the work piece firmly mounted on the carriage,
• the carriage advancing along the lathe bed to produce the length of the bore.

With this setup one can be sure of getting a non-tapered bore. The axis of this bore is of course parallel to the axis of the lathe bed and not to the axis of the boring bar. Offsetting the tailstock (horizontally say):

• will not alter the diameter of the circle followed by the tip of the tool bit;
• will move (horizontally) the centre of the circle followed by the tip of the tool;
• will disalign the axis of the boring bar from the axis of the lathe bed; thus the projection of the circle followed by the tool tip onto the vertical section through the work piece will be an ellipse with the horizontal axis slightly shorter than the vertical axis.

If, after making a first (circular) bore, you offset the tailstock end of the boring bar and make a second pass, then you will still have a non-tapered bore but it's vertical section will be the sum (with overlap) of the original circle and this offset ellipse. While the ellipse effect is admittedly very small, to me it seems that the error in approximating a larger circle by two overlapping smaller circles is not small.

I hope this is clearer. I also hope that it makes sense; if not somebody please sort me out!

 

[dsage]

Ian:

Given the situation as you describe it - yes the hole will become an oval or something looking like one hole next to another.

Not sure what I was thinking. I guess the other scenerio where you adjust the tool stickout on the boring bar but don't move the bar. (The normal situation)

Everyone can straighten ME out if I'm confused too.


Sage