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November 21, 2019, 23:39:46 pm


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Author Topic: OT: Measuring Tools - 2 Related Topics  (Read 212 times)
Bob La Londe
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« on: November 09, 2019, 17:06:20 pm »

Topic 1;  Tool length for use with tool tables.  

Its sort of off topic.  Machining related, just not directly CB related.  I've got a couple height gages.  A digital one with a USB output I use for measuring tool heights for the Tormach mill.  Because they register against the spindle nose its pretty easy to measure them. I've got a small granite plate with a hole it.  I zero to the plate and the spindle nose for reference.  

HOWEVER, with my new ISO20 spindles that's not practical.  They do not reference against the spindle nose.  They register on the #20 taper.  The do have a ring or collar on them, but as near as I an tell its only purpose is to hang them in a tool changer.  I don't know how consistently they are machine in relation to the taper either.  I have Chinese made ones and America made ones.  (The Chinese ones are surprisingly good.)  Even if they were very consistent they might not be consistent from one MFG to another.  

My answer after reading this thread on Practical Machinist...

https://www.practicalmachinist.com/vb/cnc-machining/fixture-measure-tool-length-erickson-30-taper-232446/

… is to machine a taper fixture to set the tool holder into, and set up a permanent physical tool zero for reference rather than using the spindle nose.  I've already made the fixture on the lathe, but I have not tested it yet. If you want to read about making it I wrote it up in a rather long post over on Home Shop Machinist.  

https://bbs.homeshopmachinist.net/forum/digital-machinist/1837594-iso20-taper-measuring-fixture

I'll be doing some practical testing today to see how consistently it measures the same tool, and to see if cut tests match measured length relative to tool zero.  Yes I know I could have just measured every tool in the spindle, but often I have the machine running while other tools for the job need to be loaded in a holder.  Also, measuring the 20 or so tools I need for each machine would take a lot of time on the machine.  I can do it on my surface plate with a height gage and a ground flat scribe pretty quickly, and just jot them down on my note board as I go.  (I have small paper sheet size whiteboards I use in the shop for things I don't need to save.  That way I don't wind up with piles of notebooks full of data I will never need again.)  

Hopefully it goes ok.  If the tool holder sits pretty close to perpendicular with the base of the fixture cosine error should be insignificant.  I think even a couple degrees would be tolerable.  

Topic 2:  Height Gages

I have two height gages.  One is a digital with a USB port that can record data directly to the Tormach mill.  I don't use it that way, but I tested that it work.  The other is a dial and mechanical digital dual column I have owned for a couple years, but never used.  In fact when I finally took it out of the packing I found the scriber was missing.  The reseller said when they get some in they will send me one, but in the mean time I found a ground carbide one that fits nicely in the clamp.  

All I have ever used my first height gage for is measuring tool heights, and marking layout lines for manual machining.  The second one has never been used as of yet.  I'd like to mount an indicator in it and use it to check the perpendicularity of a blank mounted in a tool holder in the new taper fixture I made.  I do have a ground cylinder gage and a granite square I can check the height gage against.  My issue is mounting a test indicator on the height gage.  It JUST has a simple box clamp.  Both of them.  All my test indicators have either a dovetail or a tiny pin for mounting.  The newer ones have both.  My thought is to just make an aluminum split block that I can put in the clamp on the height gage.  It might work for this application if I use a spacer between the base of the height gage and the tool/gage/square, nut it would be a limited application for this type of measuring only.  I was wondering if there might be a better more universal type of mounting system I could use.  

I did also consider drilling a hole in the side of the clamp, but I fear that it might introduce some error in the clamp it self if it was not stress releived before it was ground.  I still need it to be accurate when using it for measuring height.  If it twists the bottom of the scribe might no longer be perfectly parallel to the base when clamped up.  

I figured I could also use the setup to measure how parallel the top of the fixture is to the bottom.  Its not important to this application, but it would be nice to know how good of a job I can do on the lathe when I take my time and take care.  It would also give me two references as to how perpendicular the lathe is capable of cutting.  Just for added measure I figured I would very lightly stone the top and bottom of the fixture.  

Conclusion:  I think the fixture will be adequate regardless, but I can learn a bit in the process and learn some of my and the machines limits and capabilities at the same time.  
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Bob La Londe
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« Reply #1 on: November 10, 2019, 22:22:51 pm »

Ok, I couldn't help myself.  I had to check.  I used a writer erase marker on the taper (thinner than bluing), dropped it in the fixture and held it in tight while giving it a span.  It wiped off about 90% of the marking.  Its not perfect, but its certainly better than I expected.
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Bob La Londe
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« Reply #2 on: November 13, 2019, 15:04:11 pm »

It was said in another thread that this could have been done better with a sine bar.  How?  

So how exactly do you clamp a sine bar to the side of a round tapered tool holder?... and how do you make sure its straight to avoid cosine error.
****************
Why would you want to clamp sine bar to a tool holder?? You mount the sine bar in such a way so you can indicate/align the compound slide or the taper attachment correctly. It is usually cumbersome process,My lathe have an taper adapter so it is relatively easy process to use sine bar. Otherwise place sine bar against the compound slide, rig up some sort of parallel to support the bar and blocks.. Good luck.

So you build some sort if stack up to lay the whole thing on its side on the saddle to parallel the compound and match it to the tool taper held between centers?  It does sound like a cumbersome process.  Sounds like a lot of bits and pieces when one(*) indicator does the job.  When it reads zero movement over the length of travel the compound is parallel to the taper and accounts for any error in the lathe itself.  Even a cheap import lathe can turn as accurately as its mechanical limits and quality of construction allow that way.  

I guess I am just missing your point.  Was it to disparage the use of a little math to calculate the angle so I could get the compound close before bumping it into line?  I suppose I could have dug out my 1942(**) issue of the Machineries Handbook and tried to look up the angle on an ISO20 taper, but I might still be looking.  I'm pretty sure an ISO20 taper isn't in it, and I do not know that any old #20 taper is the same.  It might be, but I do not know that.  

(*)  I actually used two indicators.  A dial indicator to measure rise over run, and a test indicator to make sure the compound and taper were parallel.  I was pretty amazed at how quickly it went.  I was expecting to spend  a lot of time bumping and measuring, but I was pretty much dead on first try.  

(**) Yes I actually do have a 1942 copy of the Machineries Handbook on my desk along with a 1947 copy of the Production Handbook.  I actually use them from time to time.  

FYI:  I do not turn a lot of tapers.  Well not on purpose anyway.  When I have it has almost always been to match another taper.
« Last Edit: November 13, 2019, 15:12:58 pm by Bob La Londe » Logged

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Dragonfly
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« Reply #3 on: November 13, 2019, 18:39:56 pm »

Here is a solution of mine which is far from sophisticated but does a very good job. Recently I had to do a batch of very fine parts, back and face, with the largest tool diameter being 2mm. And a lot of tool changes imposed by the order of milling.
So I made a simple tool touch plate. The base is an insulation material (glass fiber and resign) 10 mm thick. Below the retainer ring is a steel "pill" (don't know its name in English) which are used to set the valve clearance in a car engine. Under it is a brass disk with soldered wire and a spring which holds it in contact with the "pill". The positive end of the 'Probe' input is connected to the wire. The negative - to the chassis. So the tool touching makes an electric contact.

I had to add an additional DRO to the standard Mach3 screen set in the 'Settings' tab below the coordinates of the touch probe. There I enter the measured difference between the touch plate surface and the stock surface. Once the right numbers are entered a macro I wrote for Mach3 reads them, moves at safe Z to the probe coordinates in machine coordinate system (G53), waits for manual tool change and confirmation, then plunges down to the height I've given and from there does a G31 probe at slow speed. On touching the macro sets the measured difference in Z DRO and returns the tool back to the place it was before starting the tool change.
I also added a new button in the MDI tab calling the macro because I wanted to retain the standard 'Auto tool zero' button function for manual tool touching.


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