Finding Center heigth over compound

[Niels Abildgaard]

A friend has asked for a tangential holder.
My holders are one lathe holders and as he is new to his lathes here is how I measured mine.
First picture is a piece of scrap alu and a CCMT holder ready for action.
Smooth turned all over is next
Third picture shows that two feeler blades and two leaves of kitchen foil will pass under.Three leaves will not.
Thickness of bundle is measured with micrometer and gives 1.58 mm.
The smooth turning is 47.12 measured with digital caliber (and two hands)
47.12 divided by 2 is 23.56 plus 1.58 is 25.14 mm

 

[WOB]

#1 A few tenths of a mm one way or another is not going to make a difference since you cannot account for machine and workpiece deflection.

#2 Why didn't you just chuck up a piece of rod and turn a sharp point? Then measure the height directly with a caliper or height gauge.

WOB

 

[BaronJ]

You don't even need to do that ! Just measure to the pip left when facing off.

 

[RonGinger]

It is much more accurate to measure the diameter of a round with a micrometer than it is to try to determine the exact height of a point or a pip over a flat surface. You have no positive way to set a caliper leg on the center.

 

[Niels Abildgaard]

I have given my QCTP system away and do not miss it.
My homemade tangential ,carbide insert and cut off tools are miles better (more rigid ) than anything I can buy.
For making the toolholderss it is nessecary to know the distance precisely and that is the purpose of the method mentioned.
For users with QCTPs it is not nessecary.

 

[BaronJ]

I use this ! Though a few thou makes little difference.

 

[GLCarlson]

It is much more accurate to measure the diameter of a round with a micrometer than it is to try to determine the exact height of a point or a pip over a flat surface. You have no positive way to set a caliper leg on the center.

Yep. Even easier if you have a height gauge. Turn a known diameter (or accurately center a piece of ground rod of known diameter). Use height gauge to measure height from the TOP of the round to whatever (saddle, ways, etc). Subtract one half the diameter. Distance from center to surface known to the accuracy of your measurements.

 

[goldstar31]

Yep. Even easier if you have a height gauge. Turn a known diameter (or accurately center a piece of ground rod of known diameter). Use height gauge to measure height from the TOP of the round to whatever (saddle, ways, etc). Subtract one half the diameter. Distance from center to surface known to the accuracy of your measurements.

Actually in the absence of one a cheap vernier can be used on a stand of sorts such as a bracket. Obviously, it takes a bit of thought but that's the fun.

For the really deep thinkers, utilising a top slide as a measuring device is possible. I have an old one on a tool and cutter grinder- on a rotary table- to do ball handles.

Oh, and for the non smokers, cigarette papers of a known thickness are quite useful for setting this sort of thing up. A bit of spittle and when the thing comes off on the tool- but most of you will do this already.:hDe:

 

[deverett]

The great GHT described one of his early tools - a tool height setting gauge. I know there have been dozens of different designs over the years, but his method of checking the height was simple and foolproof.

Hold a large disc in the chuck - a faceplate would be ideal. Scribe a line at the edges with your tool height gauge. Now rotate the disc 180 degrees and place the point on one end of the previously scribed line. Move the gauge to the other end of the line and mark. If you are on centre height, the lines should coincide. If not, the error will be 1/4 the distance between them.

Dave
The Emerald Isle

 

[barnesrickw]

Do the cheapie Harbor Freight digital calipers serve well for making your own height gage?

 

[goldstar31]

Do the cheapie Harbor Freight digital calipers serve well for making your own height gage?

Probably they are sufficiently accurate to be used on machine tools which are- not terribly accurate any more. You can go out and buy a height gauge that is accurate to a millionth of a thous- assuming that you have a key to Fort Knox but if you have a lathe or a mill that makes rattling good fits- why bother.

Always remember that the first steam locomotive was bored so accurately that the foreman's hat was stuffed in to seal the pistons. I still have a brass two foot rule accurate to sixteenths- give or take a week.:hDe:

 

[BaronJ]

Do the cheapie Harbor Freight digital calipers serve well for making your own height gage?

Hi Rick,
The ones that I used were one purchased from Lidl supermarket when I was in France a few years ago. Since then Aldi and Lidl in the UK seems to have them on sale for about £9 every few weeks. They are pretty good for the money, though you do need to use the Silver Oxide batteries. The ordinary, alkaline ones don't last very long.

The hight gauge that you seen in my picture uses a length of quarter Whitworth threaded rod and the nut is made from Acetel using the split plastic rod, vice and heat technique, this creates a nut with essentially no backlash.

I used bearings salvaged from old hard disk drives at the top and bottom. It works very well, calibration and repeatability can be checked and confirmed using gauge blocks.

 

[barnesrickw]

Thanks guys.