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[How do I?] Tool Change Heights

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benster

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I have a custom built CNC on "permanent" loan from a friend. He used an ER-16 straight shank holder as the basis for his spindle. As I've gotten more familiar with CNC machining on my converted G0704 I'm used to using multitool programs with up to 5 or 6 different tools. That machine utilizes the Tormach TTS however. Hands down the easiest way to continue using it is to break the program up into tool specific chunks, and run each program after a tool change and height offset. I would like something a little more streamlined. I'm thinking a tool height setter that would just probe the tool height before each op. I assume this is possible via macros? I have not set up any in LinuxCNC yet, nor do I have the tool height setter.

This had got me thinking, are there any style holders with straight shanks for smaller tools? Something similar to the TTS but to be held in smaller ER collets?

Long term it would be cool to make a new BT10 taper spindle, but this would entail replacement of the entire spindle as I wouldn't want to disassemble the existing one.
 

T Bredehoft

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Commercial (professional) practice is to install a standard spindle which accepts a "patented" tool holder. using standard tool holders you set up individual tools each in its own holder. Then you can assign a number to each holder and establish a tool length for it.

BT10 taper spindle I guess you've considered that. Any way, with collets, your set tools won't repeat.
 
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benster

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Right, thats what I do in my other CNC mill currently with the Tormach tool holders. Since this spindle is an ER-16 collet holder I currently have no way to maintain constant tool length data between tool changes. I guess one option would be to make my own set screw tool holders using the ER 16 taper dimensions, then the collet nut would clamp them in place. Would work well for small tools but would reduce my available z height which is already pretty limited.

I've seen on professional machines though where they check the tool height every tool change, usually when they're concerned about wear.
 

RJSakowski

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Right, thats what I do in my other CNC mill currently with the Tormach tool holders. Since this spindle is an ER-16 collet holder I currently have no way to maintain constant tool length data between tool changes. I guess one option would be to make my own set screw tool holders using the ER 16 taper dimensions, then the collet nut would clamp them in place. Would work well for small tools but would reduce my available z height which is already pretty limited.

I've seen on professional machines though where they check the tool height every tool change, usually when they're concerned about wear.
With the limited maximum tool size of the ER 16 collet, you don't have much in the way of options. I don't see any way to mimic the TTS capability. Your idea of set screw tool holders would be limited to small diameters as the o.d. on the socket would have to allow the ER 16 collet nut to slide past.
If it were me, I guess that I would resign myself to setting tool height every time I did a tool change. With one of the electronic tool setters, it wouldn't be too onerous. I had run a part on my old mill/drill where I had 35 tool changes. I had made my own version of an electronic tool height setter and had designated the DRO absolute coordinates to the tool height setter. I would set the tool height and rezero my absolute z axis coordinate which would effectively set my tool height for all my other work offsets. I had tried to do something similar for my Tormach using Mach 3 but couldn't find a way to make it work at the time.

I did a little playing around and it appears the the G52 command might do the job. A change by G52 affects all workplace offsets. Here is a suggested protocol.
1. Choose some means of zeroing on a reference surface; electronic tool setter. cigarette paper, dial indicator, etc.
2. Select an unused workplace offset e.g. G59 and zero all three axes on the reference surface with a master tool
3. Select the appropriate workplace offset for your machining and zero the z axis with the master tool. Repeat for any other workplace offsets.
4. When a new tool is installed, select the reference workplace offset and touch off the tool on the reference surface. Enter G52 Z0 in the MDI. The Z axis position should change. Enter G52 Z[new z position]. The Z axis position should now be zero.
5. The new tool is now zeroed for each of the workplace offsets.

While this still requires zeroing the tool with a tool change, its advantage is that the original work reference can be removed with a machining operation. I was playing with this in Tormach PathPilot but it should also work in LinuxCNC and Mach 3. Please verify before using.

My choice for tool setting is a digital dial indicator. This wouldn't be practical in the case of your ER16 collet chuck. However, it really isn't necessary to have a master tool. Your first tool or a pin, for that matter, could be used. The important thing is to zero out the reference surface and all of the intended work spaces
 

Mjohnson

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Do a search for a 5C collet stop. It's the wrong size for your ER16 straight shank spindle, but the idea is simple. Thread the back side of the ER16 spindle and make a threaded rod that comes up from the back side of the bit. The rod would have to be smaller than the largest diameter tool. Use a jam nut to set the depth of the stop rod. When setting a tool in place, push it up until it stops against the rod, and then tighten the collet. I've also seen collars used to set tool depth. http://www.pcbsupplies.co.uk/content.php/68-Distance-Rings-Mills
 
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