Bore Gauge (Stew's Interpretation)

[sbwhart]

Marv's bore gauge thread http://madmodder.net/index.php?topic=1771.0 infected me with  it was one bit of kit that I could see I was going to have a use for, and as I'm stills waiting for bits to be delivered for my next project I thought I'd give it a go.

First job Crap o Cad with some ideas of how I could adopt the design for my own needs, I've got a 5 to 25 bore mic so that range is covered I wanted something to cover sizes above this.



As I'll adopt and change things as I go along things may change from this sketch.

First job the stem

This is one of those jobs that doing things in the correct sequence is important to get thing lined up and square.

Mill flat along the length



Then with this flat against the vice jaw mill a 2mm groove along the bar this will act as slide way for the movable arm to keep it in line.



Next job dove tail for the clock I don't have a small dove tail cutter, but I do have some small boring bars, I had the idea of using them as a fly cutter but I soon realized that they were too big to use like this, so hit on the idea of using them as a shaper, set the job up vertical mill a 1.5mm deep 5 mm slot across the middle mark it up with some blue so I can see what's happening and with the tool held in the  drill chuck wind the mill table back a forward and nibble out the dove tail. Worked like a dream got so absorb with what I was doing forgot to take pics 

Here's a test piece



And the clock clamped to the bar



Have fun

Stew

[Maninshed]

Wow cool gadget, I've got to bore the cylinders for my Holmside loco soon, think I might knock one of those up, thanks for sharing the idea. 

[arnoldb]

Good going Stew 
And nice improvisation 

Cheers, Arnold

[chuck foster]

now thats a neat idea.................now yet another project for me to make 

thanks stew 

chuck 

[sbwhart]

Ok her we go again

For the spindle I used a bit of 12 mm mild steel bar, because I will be working over a relatively long length, I decided to screw cut the threads (5\16 * 32 TPI  ME and 1/4 * 40 TPI ME) to get things going straight and clean up with a die, a bit of a cheat.

My lathe has a metric screw thread so you have to set the gear chain up with a 125/127 change gear, these are the gears



the change gear is the one in the middle

And the gear train in the lathe, what your basically doing is linking the spindle up with the lead screw so that the two turn in a relationship thats gives you your thread pitch



And this is the lathe set up, because my lathe doesn't have a split nut, it stays engaged all the time, and the slowest speed I can set my lathe to is 70 RPM when working up to a shoulder its easyer to have the lathe in revers, with the tool at the back and to cut left to right away from the chuck.



I also put a 5 mm length M5 thread on the end to take a turning knob.

The other bits were just plain milling and drilling.

Two small bits of 3mm guides of silver steel were stuck in place with Loctite to a



This is it nearly finished I used a bit of hex loctited to the spindle for the handle from Marv's thread one flat would equal 0.001" ish



I thought of using a ball bearing for as an anvil but don't know how to fix it, as anyone got a 3/8" ish ball with a hole in it ?.

Cheers

Stew

[NickG]

Stew,

Will be a useful bit of kit. Good work with the dovetail, I did a keyway slot in the lathe by similar means, winding the carriage back and forth, never thought it would work but it did!

  Maninshed, a good friend of mine built holmside ... that is 1 powerful engine! Heavy too though!

Nick

[bogstandard]

Stew,

Instead of a ball bearing (I can drill you one if needed, I've got a load) I used a very small glass bead on the end of my DTI for ages when the ball broke off, just stuck on with a bit of superglue. Again I have a load of tiny glass beads if you want some.


John

[sbwhart]

Hi John

Never thought of a glass bead, great idea. 

Cheers

Stew

[sbwhart]

Taking Johns advice to supper glue a ball in place, this morning I had a look at what I had available, some 3/16" balls and a 3/16" ball end mill, first i cleared some of the meat away that would get in the way with a chamfer tool then careful to get the correct position I mill a small domed seating for the bearing and stuck it in place with supper glue.



Left it for a couple of hours to do its sticking thing, and this is what I got the ball is nicely stuck.



Her I'm setting the gauge for boring out the seating for the bearing first measure the bearing lock the mic up then adjust the gauge so that the clock reads zero, the verier adjusting screws make for nice fine adjustment:- thanks for showing this Marv.

Have fun

Stew

[Darren]

Guys, can you help me out a little here....I'm having trouble seeing how this tool can give accurate results.

Yes I know about setting the dial to zero with mic's/calipers etc, but if you don't hold the tool truly square to the bore being measured then the readings will be false surely  

I'm thinking you need a much bigger arc than the 1/8 ball provides, so that you have some leeway to being off square?

[sbwhart]

Hi Darren

Your quite right these are not easy to use you have to rock them back and too in order to find the high spot, like a pair of internal calipers.

Stew

[Darren]

Thanks Stew,

But I still can't see that working...maybe it's just me and I need to try one....

What I'm thinking is while you are rocking to find the widest spot you will also be moving in and out of the bore. The changing angles whilst doing this will give false readings due to not being square.

[NickG]

Now you've mentioned it, I can see the same issue Darren, you would have to move it around until you find the smallest distance which will be the diameter, only trouble there is, you might not be central in the bore either.

That's why a bore micrometer has 3 legs surely?

See C-o-C 2.1 .. sorry for my dodgy sketch but it makes the point. Both the sketches on the left have to be satisfied to get a correct reading. I guess the spiring loaded dti will help you find the center, then you'd need to carefully wiggle up and down a bit to get the minimum once happy it's centralised?



Nick

[Darren]

That's exactly what I was thinking Nick....

I have two types of bore gauges, one uses three legs as you describe and the other type uses large radius's on the anvil ends.

I can take a picture later if it helps.

[Majorstrain]

Hi Guys,

Maybe two balls might help to keep it square? Then you only have to worry about being central. That would be indicated by the max reading.

Just my $0.02 + GST worth.

Modified you drawing Nick, hope you don't mind. 

Cheers 
Phil

[Darren]

Nice.......

[Bernd]

Back when I worked in the grinding dept of the company I used to work for they taught me that you rocked the bore gage around and took the smallest reading. When this was done the non-movable leg of the gage was at the bottom of the bore and the movable leg was at the top. Then you rocked it back and forth and side ways and took the loweat reading on the gage. Very accurate but took a bit of practice.

Nick, you have it almost right. Just turn your "CORRECT" end view C-o-C 90 degree couter clockwise and you'll have it.

Bernd

[NickG]

Bernd, but if it's not central you could still have a smaller reading. However, I guess with practice and the fact that it's sprung loaded would help you find the centre.

Never the less, looks like a great job and once you get used to it am sure it will be an invaluable bit of kit.

It'd be interesting if you could do a few trials to see how repeatable it is against a normal bore micrometer.

Nick