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23-04-2011 #11
This is what i made for drilling, ground all over and i have different size bushes made for different size drills etc
I had to make one particular holder be perfectly ground as the slots can be surprisingly a long way off.
Agree the toolplate would only suit small parts and be time consuming to set.
Phil
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23-04-2011 #12
The trick is to make a toolplate for each job.
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23-04-2011 #13
Looks good, you have a surface grinder then? Or are you using a toolpost grinder in the lathe to do it?
I've just been and tested the holder I have with a Mitutoyo 0.0001" DTI. It seems pretty close to me, but then it clearly depends on what you consider close! I took several readings and averaged them...
Measuring on the lower surface, where the tool sits parallel to the bed the width is 18mm and I get a maximum variation of 5.2 thou at the back of the holder, 4.4 in the middle and 4.0 thou nearest the tip (0.132, 0.112,0.102mm respectively). That's going to affect the side rake of the tool by about 0.4 degrees. It's lowest nearest the chuck.
Now measuring on the lower surface parallel to the cross slide over the 98mm length of the holder, so affecting the tool rake angle. I get 6 thou nearest the tailstock (in the corner of the holder), 5.5 thou in the middle and 7.2 thou nearest the chuck (0.152,0.140,0.183mm respectively). That's going to subtract about 0.09° from the back rake angle.
The next thing I measured was the tool centre height repeatability. I zeroed the dial at the front of the holder, near where the tool tip should be. Taking out the holder and replacing it without rotating the toolpost itself I get less than 0.1 thou (0.0025mm), variation (can barely measure it). If I take the holder out, rotate the toolpost around a bit and replace I get a fraction over 0.1 thou (reading between the lines on the dial!). If I take the holder out and put it in a different position in the toolpost I get +-2.5thou (0.064mm) variation in centre height. I think that's pretty good - better than 0.01mm.
If I push and pull hard on the toolpost I can get the centre height to deflect by about 2 thou.
The last thing to measure is how repeatable the holder is moving parallel to the cross slide, i.e. directly affecting the diameter.
Edit: Measured that now and I get 0.3 thou variation, maybe 0.4 ... hard to tell, under 0.01mm.Last edited by Jonathan; 23-04-2011 at 12:29 PM.
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24-04-2011 #14
Well you could take longer to make the toolplate than to do the job.
Thanks, yes i have a Jones & Shipman 540 surface grinder, FYI a toolpost grinder would be used to grind round stock, but i have a cylindrical grinder to do that.
Any grinding on a lathe is to be done under caution that grinding dust gets everywhere if your not careful, with serious consequences.
Phil
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24-04-2011 #15
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24-04-2011 #16
But can you hold the piece to be ground on a magnetic chuck with only light magnetic force so as not to distort the piece to be ground. Then clamp to an angle plate to get it square.
Can you take a CUT of 0.000005" yes that's not a mistake, on the lathe with a toolpost grinder, can you get a part of 6" x 18" flat with a tolerance of 0.0001"
If you can then yes you can do surface grinding on the lathe.
Phil
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24-04-2011 #17
I'm not saying it will be as good as a lathe, of course not. If it was you wouldn't have a surface grinder!
You can take pretty small cuts though. The dials on my lathe are graduated to 0.001", you're cutting a 200th of that so put the top slide at an angle of arcsin(1/200)=0.29° (ok that's tricky to set) to the face. Clearly in practice that method has limitations - if you want to take a reasonable amount off then you're going to run out of travel and have to keep setting it.
There was a surface grinder at school, rarely used but useful when it was. One thing they did with it was to turn the old blades from the power hacksaw into parting tools for the wood lathe.
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24-04-2011 #18
[QUOTE=M250cnc;21885]Well you could take longer to make the toolplate than to do the job
obviously this is when he goes to cnc.
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24-04-2011 #19
I will at least make a rear parting tool holder since I use the parting tool on almost every part.
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24-04-2011 #20
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