cnc shaper

I'm wondering if I'm over thinking the need for the gib lock. When I think back I've seen many a shaper user hand down feeding with no apparent problems. Maybe the need to lock the gibs is only on a flat surface. When I think about it my discovery that things went out of flat was over inches of X travel, not for a while. And it was flat for who knows how many strokes at .005 per stroke. After I put the manual gib locks on it like Frugalguido's that stopped. So I probably am overthinking the need for the articulated gib lock if I'm downfeeding. It is fun to think about though :)
 
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You may not need a gib lock but when down feeding it does tend to hold up then drop the slack out of the feed. Thats where a processor could over feed then pull back up to the desired depth, eliminating the backlash. Its a fine line adjusting the drag on the gib to stop the cutter pulling down and still move the thread smoothly.

Greg
 
Would a ball screw be feasible?
 
Probably, I have no experience with them. The concept of over feeding and coming back was on one of I think his name is Stephan's (the German chap, incredible machinist) videos where he used a stepper to control a rotary table, if he wanted to go backwards he used this concept to remove the backlash in the worm drive.

Greg
 
Of course this is all beyond my payscale, but with a rotary table I would think you'd backpedal because of all the weight and inertia taking up your play possibly. I wouldn't think there would be as much inertia with the cutter head. I guess if you had all this programmable it would be more possible to step your next cut, backpedal and step back all while the ram was on the return stoke. Doing it mechanically, wow.

One thing that would be very handy would be an electronic stop, especially if it was DRO controlled. Probably already have it and my Luddite self doesn't know it. I love that I can set up the shaper and go do something else and just keep an eye out but it would be better if it would shut off. I guess it's not hard to rig a stop switch. But I'm so electronically phobic and lazy I'd rather keep an eye out.
 
The electronic lock is something I've wondered about for my electronic dividing head. I copied: http://www.liming.org/millindex/
I added the snailworks electronics to my Harold Hall dividing head. The stepper is oversize with the idea that that is the locking-holding power.
But I usually lock the manual lock when cutting anyway. If it locked after rotation and unlocked before rotation by itself it would be handy.
A rotary actuator and some extra programing on the arduino would probably do it. I'm just not to good with the programing part.

Same kind of setup could lock the gib. Be it actuator, solenoid, or even a stepper. Probably need some linkage and possibly some spring loading also.
 
I've put a bit of thought into CNCing a shaper. I wouldn't be in a terrible hurry to control the tool angle. You can cut angles and shapes using the cross and downfeed, you will likely need to use multiple tools to do complicated geometry anyway. Here are the requirements that I came up with:

1. No need for ballscrews. My plan was for a retrofit, so finding room for ballscrews would be a problem anyway, but there is no need. You are not cutting circles or complicated shapes such as in a mill, and you are always approaching the cut from the same direction, backlash compensation will work fine.

2. The drives need only be fast enough to make the maximum move during the highest stroke speed. In other words you will only be moving the the motors before and after the cut, not during.

3. There is no need for a clapper. You can retract the tool away from the cut at an angle before the backstroke starts and advance it before the cutting stroke starts. How fast you can do this will determine your maximum cut/stroke (also the lead in/lead out of the tool is part of this equation).

4. As with any CNC machine, changing tools quickly will be key to this machine being useful or a novelty. A quick change tool system will be needed.

5. Since you will need to be able to figure this out in some sort of CAD/CAM, standardized tools will be needed. This is one are that begs for inserted carbide. Not often used on shapers and planers, it doesn't mean they can't be. Grade would need to be as soft as possible to withstand the interrupted cut.

6. A fancy custom controller is not needed. A Beaglebone Black running machinekit was what I was thinking of using. You would need to put some sensors on the machine to give positional feedback of the ram in addition to the normal limit switches.

7. The real problem is the CAD/CAM. You only really need the G0 movement code, as you will always be moving the tool at the max the drives can move it. Figuring out that movement and writing the G code efficiently is the problem. With my limited software skill/desire/patients for programming I was thinking of doing something in Excel that would allow you to string together facing at angles, slots, curves and dovetails to build the code for the machine. I'm sure someone else out there has the skills to do something much better than that.

I already have the test subject to try this on, an 8 inch Lewis kit shaper. But there are many more projects ahead of this one, so I don't expect anything to happen on it anytime soon. If it worked on well on the Lewis, I was going to put it on my 16" G&E and really move some metal.
 
I wonder what scale would be good to do a prototype with?

quick change tool holder is a great idea!
 
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