Making a center height gage to set lathe tooling

[precisionworks]

There are as many ways to set lathes tools to center height as there are machinists. I sometimes use the Circle Machine Company tool shown below, and it works well in those situations where it physically can be used.



There are lots of other times that there's no room for the Circle Machine gage ... so I built (another) simple center height gage. As shown below, only three parts are needed - two pieces of ground flat stock & one piece of round stock. The round stock is cut slightly long and a sharp live center point is used to mark center height.

The round stock is faced off so that the scratch mark is still intact. The parts are laid one on top of another & center height is checked. At this point, the flat surface should be too high, leaving room for final machining.

The round stock is center drilled, tap drilled, & countersunk:

With the spindle set to the lowest rpm, a Balax Thredfloer forming tap is held by the Jacobs Super Chuck in the tailstock. TapMagic is squirted into the hole & flooded over the tap, the spindle is started & the unlocked tailstock is pushed forward until the tap engages. I keep a foot firmly on the foot brake & step on the brake as soon as the tap rotates in the drill chuck. Balax tap shanks are quite smooth & hard as glass, and the Jacobs chuck allows the tap to turn no matter how tight the chuck is. If you use an Albrecht keyless in the tailstock, don't expect it to let the tap slip Some people will stop power threading after the tap has engaged three or four full turns & finish with a tap handle ... probably the best approach.

The three parts are put together with a pair of flat head allen screws. The reference edges are brought to a sharp 90 degrees on the surface grinder.

The top surface is ground down until it is .010" higher than lathe center - this flat is used to set ID tooling (boring bars, etc.) The other end is ground down an additional .010" until it's at dead center (see the step at the front of this photo). The "step" is used to set OD tooling:

Using the tool is simple, bring the point of an insert next to the reference flat & use a small straightedge to sweep the top.

Finished gage in use.

 

[Energie]

Hi Barry,

a very usefull tool, and a really solid construction.


I´ve made a small one for my mini-lathe:

Another version with an usb-microscop-camera.

0,15 mm too deep:

Ok:

 

[precisionworks]

Another version with an usb-microscop-camera.

That is kewel :twothumbs

That's the first optical tool presetter I've seen that was shop built ... most cost a few grand:

http://www.fvfowler.com/opreset.html

 

[wquiles]

That is kewel :twothumbs

+1

Very cool indeed :twothumbs

 

[PhotonFanatic]

I'm curious as to how precise using a straightedge, checked optically by the human eye with a machinist's square, between the cutting edge of the tool and the piece turns out to be. Anyone seen some numbers on that technique?

 

[precisionworks]

how precise using a straightedge, checked optically by the human eye with a machinist's square, between the cutting edge of the tool and the piece turns out to be.

The eyes can be closed, as the straightedge is swept back & forth while raising the toolholder block while feeling for contact. The Aloris & Dorian holders use a 24 pitch screw, so each complete turn of the adjuster nut moves the tool .042", or roughly .010" per quarter turn.

It's pretty easy to move the tool point up about .001" at a time as the tool point gets close to center height. One time the straight edge sweeps across the flat & contacts nothing, then the nut is turned slightly & the straightedge makes contact that can be barely felt ... I'm pretty confident that the point can be brought to center +/- .001", but that depends on a delicate touch.

If a person gets in a hurry, center could easily be missed by a couple of thousandths either way.

If you have just a few toolholders, this may not be the biggest problem you encounter. I currently have 24 Aloris or Dorian blocks, each loaded with a tool, and the center height gage surely makes life less stressful :thumbsup:

 

[gadget_lover]

I would suspect that the straight-edge method is fairly accurate, especially when used with a sharp tipped tool. When combined with a machinist square, you can get it pretty close.

I use that technique and more often than not the tool will face without leaving a nub.

For things that are not cylindrical, the height setting tool would be quite handy.

Daniel

 

[precisionworks]

For things that are not cylindrical, the height setting tool would be quite handy.

It's funny how certain events motivate a person to spend a couple of hours making a gage or fixture ... in this case, the Aloris #20 tool holder is the the culprit (see http://www.candlepowerforums.com/vb/showthread.php?t=277766 )

The #20 is one of the most used tools in the box, but it has one drawback - since the insert face is usually tipped in the direction of travel, the height of the point varies as the point is rotated from that one setting. The brain dead solution is to set the tool at the "middle" setting mark, meaning that the rake angle is wrong 100% of the time but the point height stays constant. Instead, I made the gage & will likely use it more often on the #20 than most other tools.

Boring bars are the other tool that needs frequent recentering. Every time the bar is lengthened or shortened from its current setting, the point has to be reset. If the same bar is always kept in the same block, the height adjuster nut will stay locked in place and the bar is rotated to bring the tip on center +.010" higher. If you ever try to bore with a bar that's even slightly below center, causing either the bottom of the insert to rub or the bottom of the bar to rub, you'll quickly find that it's no fun. Same thing if the point is too high, as the angle of attack between the tool point & the work changes greatly when the tool is much more than .010" above center.

 

[PhotonFanatic]

For only $22, this tool setter might be nice to have on hand. Would be better if it had a digital readout. :devil:

 

[precisionworks]

That's a neat idea :thumbsup:

American made, which is always surprising, at a low selling price. Looks like he turns those out on a Haas Mini Mill, which is perfect for smaller production jobs like the tooling he makes:

http://www.haascnc.com/details.asp?ID=MINIMILL&webid=VMC_MINIVMC#VMCTreeModel

IMO, the only thing missing from his centering tool is the "double step" that the Circle Machine gage has ... which allows either setting either on center or setting .010" above center.

 

[Energie]

Hi Fred,

thanks for the link.
After some hours in the shop:

Made of brass and stainless steel.
Quite accurate, +-3/100 mm.

 

[PEU]

Very nice craftmanship!


Pablo

 

[PhotonFanatic]

Hi Fred,

thanks for the link.
After some hours in the shop:

Made of brass and stainless steel.
Quite accurate, +-3/100 mm.

How do you set the level to be parallel with the SS rod that contacts the tool tip?

That is some nice work, BTW. How much did all the materials cost?

 

[Energie]

How do you set the level to be parallel with the SS rod that contacts the tool tip?

A short clip: Link

 

[wquiles]

Very nice craftmanship!


Pablo

+1

:twothumbs

 

[PhotonFanatic]

A short clip: Link

I understand how to adjust the tool holder, as shown in the video, but in constructing the device, what ensures the parallelism between the level and the tube that contacts the tool bit?

It looks as though there is a set screw on the level to clamp it to the main body--but before tightening that, I presume that the two pieces need to be aligned, no?

Nice MultiFix tool holder. :thumbsup:

 

[wquiles]

For only $22, this tool setter might be nice to have on hand. Would be better if it had a digital readout. :devil:

By the way, I did order one of these today. I will report back in a few days (next week?) when it arrives

 

[Energie]

I understand how to adjust the tool holder, as shown in the video, but in constructing the device, what ensures the parallelism between the level and the tube that contacts the tool bit?

There is no parallelism needed between the level and the tube, that contacts the tool bit.

First time adjustment:
- use a tool bit with the exact heigh
- set the level to zero and fix the scew
Without this adjustment, the device works not correct, if the lathe does not stand even.

 

[unterhausen]

ordered one of the edge tools. $25 shipped is not worth the time it would take for me to order a level vial.

 

[wquiles]

ordered one of the edge tools. $25 shipped is not worth the time it would take for me to order a level vial.

+1

That is exactly why I ordered mine - my time is worth more than the $25 for the finished/proven product :twothumbs