Dovetail myth regarding pin dimensions.

Outstanding answer. Thank you.
I just went out to look around my shop and the only dovetails I could find without a gib were my quick change tool post and microscope rough Z (elevation) positioning heads. The fine adj. had gibs of sort. (spring loaded ball bearing assy.)
Think I'll take your advice and "try it my way" and build a few tool holders for the quick change tool post just to see what will happen.

Thanks again.
b
 
Bruce Billett said:
Outstanding answer. Thank you.
I just went out to look around my shop and the only dovetails I could find without a gib were my quick change tool post and microscope rough Z (elevation) positioning heads. The fine adj. had gibs of sort. (spring loaded ball bearing assy.)
Think I'll take your advice and "try it my way" and build a few tool holders for the quick change tool post just to see what will happen.

Thanks again.
b
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Good luck. If I was you, I'd make one first and see what happens. If you get positive results, terrific, tell us and make another. If you get not so good results, let us know what you did, so we all can learn something. We all can learn something from what you did, and how it came out. If we share our experiences we can build up our group knowledge.
 
Sometimes, folks who are tenacious need to learn by experiencing it themselves. They either find a better way, or get a lot better sense of the nature of the problem, i.e. learn via failure. I've been that person at times. But it's usually a lot easier to examine how things are normally done and start from there. Carry on.
 
Any time you are cutting angled surfaces (dovetails or single pointing threads for example), what do you do if the cutter does not come to a perfect sharp point? Bruce you say I can just touch off on the part and use the lead screw on the mill to dial in the cut. Calculating that depth ASSUMES the cutter comes to a perfect point, but in reality, the tip has a small flat or it will after the first few passes through material.
Same thing with threads, the standard US thread has a flat on the root. So just dialing in a depth doesn't get you where you want to be. Any error in the size of the flat on the tool changes the depth required to get the pitch diameter correct. Thats why you measure threads over wires.
Measuring dovetails over pins is same same.
 
Parlo said:
I've tried my best to help, but keep getting the same banal question rephrased over and over. You can take a horse to water etc.
Over to you guys...
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Parlo, I think the issue is you don't understand the question. Most likely my fault! I sometime have issues with getting people to understand what I am asking. Mostly because I am to stupid to even know what to ask nor how to ask it. I have the instructions, I can do the work. These are not issues, so please do not fret over that. I have spent near 50 years working in the micron and sub micron world. Trust me when I say I get that precision part! I was able to stay alive in that world because I challenged accepted norms. and ask why a lot!!! Most answers I got were "here, shut up and go away, this is how it's done!" Delving into the WHY? often yielded insight for me that let me think beyond the conventional, saving much time and cost as so many thing are "done this way" because that is what you are told that and no one really knows why. Most people think inside the box, it's safe there. Some people think outside the box. I on the other hand have found I have NO idea where nor what the box is.
What I am seeking is simple understanding.
I have drank the KoolAid (water) you have been kind enough to lead me to, and found it to be wanting.
Please, let you nor anyone else take any sort of offence to this note. It is not meant to cause anyone any grief. It is just my trying to explain my questions.
Thank you all once again.
b
 
Asm109 said:
Any time you are cutting angled surfaces (dovetails or single pointing threads for example), what do you do if the cutter does not come to a perfect sharp point? Bruce you say I can just touch off on the part and use the lead screw on the mill to dial in the cut. Calculating that depth ASSUMES the cutter comes to a perfect point, but in reality, the tip has a small flat or it will after the first few passes through material.
Same thing with threads, the standard US thread has a flat on the root. So just dialing in a depth doesn't get you where you want to be. Any error in the size of the flat on the tool changes the depth required to get the pitch diameter correct. Thats why you measure threads over wires.
Measuring dovetails over pins is same same.
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ASM109
I personally don't use the lead screw for much other than movement. far to much at question. I use the DRO. As mentioned before I have an RJ mill/drill and a Chinese mini-lathe. Threads? I ain't EVEN going to go there just for fun. See my tooling! I also work in the very small area. 1/4-20 is a BIG thread for me. So I know I can't cut in that arena. Imagine if you will a boring bar for cutting a 2-56 internal thread . (Shutter at the thought!)

I thank you greatly for your thoughts on this. It is helping me understand.

b
 
Bruce Billett said:
I have spent near 50 years working in the micron and sub micron world. Trust me when I say I get that precision part!
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Did you measure those microns and how? If so, why bother measuring when you could just measure the cutter and use the dial to move over the needed amount.

I don't mean to be rude but, where are you going with this nonsense? My Grandfather was an Electrical Engineer and he couldn't wire a light switch, there's a massive difference between theory and reality!
 
Firstram said:
Did you measure those microns and how? If so, why bother measuring when you could just measure the cutter and use the dial to move over the needed amount.

I don't mean to be rude but, where are you going with this nonsense? My Grandfather was an Electrical Engineer and he couldn't wire a light switch, there's a massive difference between theory and reality!
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Measuring micron? Optics mostly There are a few tools out thee that can measure mechanically typically involving LVDT's and the like but once you get below about 3 microns, optics. Another method is sheet resistance but that is only good for thickness of a material. Also a SEM. Not much good for the real world however.
Where am I going with this? I have a feeling that someone out there thinks I don't know what I'm talking about concerning small scale measurements, and it's effect on materials. I do. That is all.
If someone is capable of answering the question and leave out the hyperbola, I will be happy with that to no end!
I tend to switch over to microns around .001". Force of habit I fear. Don't mean to offend. I am merely aware that when one approaches these numbers the room temp. has a great effect on the measurements for larger parts. Say 6-8".
Why bother when I could just measure the cutter and move? THAT my dear sir is the actual question I am seeking the answer to! Thank you for clarifying it.
I don't consider your comments rude in the least, actually most beneficial! As I mentioned before I am to ignorant to even ask the right questions! So this helps
thank you.

b
 
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