Tool indexer

[blades]

So, I took a temporary detour while working on the 7 x 10 CNC project and decided to build a tool indexer.
I had to do something with the beautiful little NEMA 17 motor from the dead HF micro lathe fiasco.

This tool indexer will hold (4) 5/16" tools. Indexing will be controlled with a 3rd axis on the G540. The 4 center drill spots in the front of the tool block are not utilized. They were originally put in for another ratchet option, but changed my mind on that design.

Looking at the front of the tool block, it will index in a CW direction. A modified 3/8 ratchet will be mounted on the back of the motor, locking the tool block from rotating back CCW. I'm working on the assumption that the indexing program will rotate CW 52 steps, then CCW 2 steps to lock the rotation against the ratchet. Sounds good in my mind, anyway.









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[eartaker]

Blades,

That is awesome I hope it works out. I like the ratchet idea.

[Fastest1]

Blades, nice work but I do have some questions. You intend to index by stepping 1 direction x amount of steps then back up onto the pawl by a few steps in reverse, correct? I think it would be best if the dro was reset to whatever the correct degrees of that tool holder is supposed to be. There will be steps lost when backing up onto the pawl, not hard on the stepper but necessary to insure the tool is the correct place. You state you are going to place the ratcheting mechanism on the back of the stepper, using the shaft of the stepper to secure the position of the tool? What will be responsible for holding, a grub screw or helical coupler. Seems like the stepper should control rotation and the ratchet should remove the load from the stepper and secure tool positioning. I would think the flex due to the leverage of the tool holder, tool and the stepper shaft will allow the tool to move under load. Btw wouldnt it be 92 steps forward and 2 reverse (I believe you were using steps in reference to degrees) for a 4 tool holder?

So, I took a temporary detour while working on the 7 x 10 CNC project and decided to build a tool indexer.
I had to do something with the beautiful little NEMA 17 motor from the dead HF micro lathe fiasco.

This tool indexer will hold (4) 5/16" tools. Indexing will be controlled with a 3rd axis on the G540. The 4 center drill spots in the front of the tool block are not utilized. They were originally put in for another ratchet option, but changed my mind on that design.

Looking at the front of the tool block, it will index in a CW direction. A modified 3/8 ratchet will be mounted on the back of the motor, locking the tool block from rotating back CCW. I'm working on the assumption that the indexing program will rotate CW 52 steps, then CCW 2 steps to lock the rotation against the ratchet. Sounds good in my mind, anyway.

[blades]

Thanks guys. Fastest, it's going to take some trial and error to get the programming right for the rotation. I hear what you're saying about programming the angle, but I don't have an encoder, so the program is ultimately going by step count anyway. The ratchet pawl has 72 teeth or 5 deg. per position. The stepper is 1.8 deg. per step, so in theory, I really shouldn't lose any steps if the ratchet is doing it's job. (BTW, I believe you have degrees confused with steps on your last comment, 50 steps = 90 deg.).

I will either press-fit the ratchet on the shaft, or use a set screw (I'd have to grind a flat on the back shaft). I'm not really a huge fan of press-fitting the ratchet wheen on the motor, so I'll probably try to find a carbide center drill to get through the case.

It's pretty obvious that this isn't going to be practical for heavy cuts, It's simply not built robust enough, although I expect it to perform decent on soft materials. I made it easy to take on/off, so it's no big deal to switch over to the standard tool holder if needed.

[Simon C]

That ratchet idear is genius, would luv to see a vid of this thing in action when its finished.

[awemawson]

Reversing onto your ratchet is a very similar idea to that used on the tool indexer of the Denford Orac lathe. They use a DC motor, drive it forwards counting pulses on a coarse optical encoder, and when just past the tool reverse the motor and leave it stalled running in reverse so it is pressed onto the ratchet. Cutting forces also press in that direction. I upgraded one a few years back, and made some electronics that did the reversing trick, then after 5 seconds halved the motor current as in the original design the motors overheated and fried themselves after a while!

[blades]

I'll definately post a vid of it when I'm done. I'll also update with more pics when I get the ratchet mounted.

[justin bowser]

Looks promising. I eagerly await your results as I have thinking about some sort of tool-change "turret" myself...

[blades]

Yeah, I was looking at a couple of different turret type options, and this one seemed the most do-able considering my limited resources (read, limited mill access).

[Fastest1]

Yes I was thinking in degrees. My Dyna lathe uses a 6 position tool changer and the stepper just stalls for a brief second when backing up just enough to insure contact with the stop. I have a tool changing macro provided by someone else. I havent used it as the lathe is in project status but it is getting closer.

[blades]

That's what I'll need, macros or canned cycles that can index 1, 2, or 3 positions.

[blades]

Ok, I ended up having some difficulty with the original ratchet setup. Concentricity of the ratchet, as well as problems trying to attach the ratchet head to the motor. The ratchet caused a bind in the rotation that I couldn't seem to resolve. Still wanting to utilize a ratchet, I decided to try something different.

I visited sdp-si.com for a shaftloc, as well as a 56 tooth timing belt for my X-axis (my original 55 tooth belt was bit short). I made a bracket that attaches to the round toolpost anchor in the cross slide, and modified a 1/2" Gearwrench. The result is silky-smooth rotation now.

[awemawson]

IMHO the rachet should be made integrally with the rotating tool holder to ensure maximum rigidity. If you mill a rachet on the reverse, it only needs a strip of stiff spring steel pressing onto it as the pawl. You reverse onto the end of the strip. Alternatively the strip could bias a hinged bar against the ratchet as the actual pawl.

[justin bowser]

Blades, looks cool so far but I think I'm going to need to work up some sort of horizontal turret as I have a boring bar I need to bring into play... I just got a small CNC router/engraver so the lathe project will be short-changed even more until I get the new toy figured out! :-p

[blades]

IMHO the rachet should be made integrally with the rotating tool holder to ensure maximum rigidity. If you mill a rachet on the reverse, it only needs a strip of stiff spring steel pressing onto it as the pawl. You reverse onto the end of the strip. Alternatively the strip could bias a hinged bar against the ratchet as the actual pawl.

My original design was going to utilize a ratchet on the back side of the tool holder. See those 4 small center drilled holes in the pic? Those were going to be used to attach the ratchet wheel, but I just didn't have enough room to fit it in behind the rotating tool holder, which is why I opted to go with the ratchet mounted on the opposite side of the motor. My access to the mill is very brief, so I can't get too elaborate with anything. I'm sure the ratchet mechanism will do it's job fine where it's at. A short, hardened 1/4" shaft doesn't have much give to it at all, and is appropriate for the application.

[jasminder]

My original design was going to utilize a ratchet on the back side of the tool holder. See those 4 small center drilled holes in the pic? Those were going to be used to attach the ratchet wheel, but I just didn't have enough room to fit it in behind the rotating tool holder, which is why I opted to go with the ratchet mounted on the opposite side of the motor. My access to the mill is very brief, so I can't get too elaborate with anything. I'm sure the ratchet mechanism will do it's job fine where it's at. A short, hardened 1/4" shaft doesn't have much give to it at all, and is appropriate for the application.

dear blight,
that is what i was thinking. It was better to mount the lock mechanism( the ratchet in your case) just behind the tool holding plate. In your design it is mounted behind the motor. So the entire locking and twisting force is on the 0.250 inch dia and ~3 inch long shaft of the motor. I know they are hardened but still not enough. It will take hardly 1/2 inch between the motor and tool plate if you mount the rachet behing tool holder.

example [nomedia="http://www.youtube.com/watch?v=njRvzHUuL1I"]YouTube - Emco toolchanger[/nomedia]

waiting to see it working from this side,
jasminder singh

[blades]

And to what degree do you think a 2" long x .25 dia. Hardened shaft is going to twist when cutting nylon and plastics, or even aluminum with a 1.25" lever? Trust me, I can live with whatever small amount of deflection, if any, I get on a rough cut.
Do you see an extra 1/2" of shaft length or gap between the motor and tool plate?
There's a reason the ratchet is on the other end of the motor, because there isn't room for it on the front.

The Emco unit is nice, but I don't have the time or inclination to get that elaborate with it right now.

[jasminder]

And to what degree do you think a 2" long x .25 dia. Hardened shaft is going to twist when cutting nylon and plastics, or even aluminum with a 1.25" lever? Trust me, I can live with whatever small amount of deflection, if any, I get on a rough cut.
Do you see an extra 1/2" of shaft length or gap between the motor and tool plate?
There's a reason the ratchet is on the other end of the motor, because there isn't room for it on the front.

The Emco unit is nice, but I don't have the time or inclination to get that elaborate with it right now.

dear blight,
i think i should have read the whole thread before posting. For alu and nylon it will be too much. But for bigger cuts the load will be on the bearings of the motor that are not designed for such loads. But because all you can loose on the game is just a small motor so there is nothing bad in giving it a trial.
for minor cuts the tool changer will be good and it is a damn simple design for mini lathes. coooool.
but because you are using the bearings of the motor, it is not a good idea also to put the rachet between the motor and tool plate. the more the distance the more the deflection.

your design will work better.
jasminder singh

[blades]

Trust me, if I had designed this from scratch it would look more like the Emco indexer, which is really nice. But this project was more of a quick project idea to use one of my motors. I don't forsee any issues for my intended use, but I'm sure trying to take a decent cut in steel would result in a good deal of deflection and tool chatter.

I still need to get a current limiting resistor for the motor, and figure out the programming. Been very busy with other projects around the house, so this has been low priority. I do want to get it finished up though.

[jasminder]

Trust me, if I had designed this from scratch it would look more like the Emco indexer, which is really nice. But this project was more of a quick project idea to use one of my motors. I don't forsee any issues for my intended use, but I'm sure trying to take a decent cut in steel would result in a good deal of deflection and tool chatter.

I still need to get a current limiting resistor for the motor, and figure out the programming. Been very busy with other projects around the house, so this has been low priority. I do want to get it finished up though.

dear blight,
i can really bet on that "tool chatter issue now". i have a tool changer that i made and is running successfully after some big and some minor changes to the design. My experience says "if there is something that flex even 2 micron, you will have tool chatter"
even if you can live with the surface finish, the noise of the chatter may disturb you. But again it depends upon the material being cut and the feed rate and rpms etc.
just run it and see and show the performance also.

i am worried if the through hole in the housing plate of the motor is very big than the shaft dia. It should not be more than a few thou than the shaft dia.

but you are amazing designer sir, i would like to know what you professionally do. Everybody on cnczone is fan of your cnc lathe (including this J). Now this amazing tool changer comes.

jasminder singh