How complex would this DIY Swiss style lathe conversion be to set up hal/ini?

Going to try and explain the project in a way that y'all can imagine as I feel like it should not be too difficult to program in linuxcnc but I wanted to hear the community's inputs

project: Regular Taig CNC lathe with the 5c headstock. I have already converted the 5c headstock to a guide-bushing-esque headstock. My plan is simple: add a second linear "Z axis" that holds a servo that spins the stock and can also move forward and back to feed the stock through the guide bushing headstock. This guide bushing 5c headstock is thus unpowered.

My thought: Could I just have this new axis be the official Z axis, and have the native tag Z axis be another regular linear axis where it simply acts as one of the offset parameters when setting tool offsets? So the only movement the regular taig Z axis would do is move when switching to a different tool such as drills or boring bars of various lengths, while the newly added Z axis behind the headstock acts as the primary Z axis.

I have all of the build details down so I don't think that will be a problem, but I want to know if you guys suspect it will be hard to code in linuxcnc. I do have experience setting up regular lathes & 3/4 axis cnc machines.

This sounds interesting, but I can see a number of challenges.

It'd be easy to define the original Z as "W" - which is interpreted by LCNC as another linear axis along Z.

Based on your description, you'd be using the new W to reposition the carriage for tool changes like a gang-tool lathe?

Assuming that's the case, one slightly tricky part - depending on your coding/cnc skill - will be setting up tool change macros.  You'll probably need to remap "T" to a macro/ngc file that moves X & W for each tool.  Idea being you never command the W-axis directly in a program - only during tool touch-offs.

You might also want to reconsider leaving the original spindle/head unpowered, presuming it still has the OEM spindle bearings and you've basically just stuffed a bushing in the spindle bore.

Without a rotating guide-bushing you will be limited to surface speeds way below desired for carbide tooling - unless you add a serious oil flow system to the guide bushing.  With the price of servos so cheap these days, consider powering the guide bushing with a small servo slaved to the main spindle motor.  That should reduce the lubrication requirements as the bushing will be rotating the same speed as the stock.

The biggest problem I see with the arrangement is that you have no Y-axis, and thus no traditional X/Y 'frame' like that used on a Swiss lathe.  Your tools will all be on the same X-axis plane so your stock/part will have to pass between the tools - again, like a gang-tool lathe.

One practical problem will be getting your tools on center.  You'll have to use shims (annoying), or adjustable-height tool mounts ($$) for all your tools insead of the Y-axis like on a regular Swiss.  Or home-made holders that you bore in-situ for round-shank tooling.

Related problem... do you have enough height above the current tool slide to pass stock over it and between tools?  I can't imagine that little thing being able to turn more than about 3/4" stock, but tool center height is something to consider.  It'll be significantly less frustrating if your center height is a 'standard' height and you can use off-the-shelf holders/fixturing.

Last hurdle... how to you plan to advance more stock once you've parted off?  Traditional Swiss have an auto collet closer in the sliding head, and a bar feeder that can positively locate & move the stock forward (and back).  Unclamp head collet, head slides back while bar-feeder stays put, head re-clamps.  At the end of the bar the collet opens, the bar-feeder pulls the remnant out, dumps it, grabs a new bar and away it goes.

Or are you planning to run one part at a time and advance the stock by hand?  If so, what's the point of the lathe?  If you want some of the benefits of a Swiss (guide bushing support for floppy parts) a traveling steady rest like Andy Pugh built would get you there with rather less work:



Not trying to rain on your parade here - just some food for thought.  Love the challenge, fingers crossed and all that.

Hey thanks for your detailed response and definitely gives me some food for thought, I wanted to respond by point:

1. Yes plan is to remap T and use a W axis, and agreed that W would only be called during tool changes
2. My initial plan was to have a bushing with radial set screws to give enough friction to have the unpowered lathe headstock spin by friction, however, I agree I think it would probably be better to just slave two servos together so I will probably do that
3. I do plan to add a Y axis with two vertical axis at each end of the X axis cross slide but that is still a work in progress to design
4. I currently do have adjustable height tool holders and will use those temporarily
5. I do think I have space to slide the stock in - my maximum stock diameter will be 1/4 inch so around 6mm
6. As far as advancing the stock - I am not sure I am picturing what you are suggesting correctly, the new Z axis will be 12 or so inches so I will have about a foot of stock loaded in at a time, most of my parts are small so each bar of stock will be plenty of parts and I will just manually enter a new 12 inch bar of stock by retracting the new Z axis and unloading it. I don't mind this part being inconvenient for my use case as I only do very small volume parts
7. MOST IMPORTANT: so I have tried a traveling steady rest - the problem is, all of the tools have slightly different Z offsets (imagine a R handed 55 deg insert tool vs a parting blade - I guess I could solve this by having even more customized tool holders such that the actual cutting point of the insert of each tool type are all exactly lined up to the guide bushing, but I found this hard to do in my previous project which is why I was trying to pursue the W axis method (in addition to it being useful once I create the Y axis

ffffrf wrote:

7. MOST IMPORTANT: so I have tried a traveling steady rest - the problem is, all of the tools have slightly different Z offsets (imagine a R handed 55 deg insert tool vs a parting blade - I guess I could solve this by having even more customized tool holders such that the actual cutting point of the insert of each tool type are all exactly lined up to the guide bushing, but I found this hard to do in my previous project which is why I was trying to pursue the W axis method (in addition to it being useful once I create the Y axis
 

I don't think you're gonna be able to get every tool exactly on the same Z point using separate tool holders.  But you can certainly set a Z-offset for each tool even without the additional W-axis.  You mount the tools as close as you can to some Z-point, and then set a Z-offset for each one to get them spot on.

The only thing a separate W-axis + fixed location bushing would help with would be getting clearance for tool changes without having to pull the partly-machined part back through the bushing.  Although now that I think about it, that'd be a pretty good reason to have one...

My ramblings about loading the stock was meant to get you thinking about the stock remnant.  Even if your Z has 12" of travel, you won't be able to cut whatever stock is inside the headstock/bushing once the new Z spindle nose is up against the back of the headstock.

Even if the bushing is only 1"-2" long, if it's mounted in the old headstock you can't cut whatever length the headstock is.  The Taig headstock looks to be about 4" long.  Add ~1" for a pulley to power the rotating bushing... so 5" long.

That's 5" of waste for every 12" piece.  If you use 18" stock it hurts less, but about 1/3 your stock simply can't be machined because the sliding headstock runs in to the back of the fixed headstock.

I suggested a traveling steady because you could build it very, very short, but still have a powered bushing.  The steady frame gets bored in place (as in Andy's vid) for a couple of AC bearings, and you make a bushing carrier 'spindle' which is just barely longer than the bushing.  The frame could even have a mount for a small servo built in.  If you get the whole thing down to 2" long, that's WAY less waste per piece of stock.

If you aren't keen on a traveling steady mounted to the X/W carriage, making a new - really short - fixed headstock would cut way down on stock waste.

I definitely hear you on the stock waste and that may be a good reason to increase my guide bushing axis to be 18 inches, however, I have a method where the actual full headstock length will not be all waste, based on how my stock will insert into the drive servo, I will get about 40% of the tag 5c headstock as usable stock, so knocking it out from 5 inches to around 3 inches.

So you are saying that with a traveling steady rest and gang tooling, I should be able to have every lathe side cutting tools (ignoring drills and boring bars for now) be able to cut right at the entrance of the bushing? I am trying to imagine this. If it is possible, in that case, during a tool change, I just need the guide bushing axis to retract the stock all the way back, and only then cause the cross slide to move to the new tool location, then the stock pops back out of the bushing and cutting proceeds? I need each lathe tool to have its cutting edge right at guide bushing entrance.

My issue is with each tool holder, your actual cutting edges will not all line up, for example, I dont want my 55 degree side cutter to be cutting right at the bushing, but my parting tool has to cut 5mm beyond the bushing just based on where the cutting edges line up in my taig tool holders.

Also, if I add a Y axis and live tooling, in that case would you recommend the W axis?

With a traveling steady you can set the Z-offset for each tool.  The end of the stock will be the same position from the tool, but the tools will not be the same distance from the steady.

If you need the tools to be right up against the guide bush, then a traveling steady probably isn't what you want.

With a fixed guide bush the W-axis can set the edge (or whatever the control point is) of the tool right up against the bush.  You would touch off each tool just like on a non-bushed lathe, and jog the W-axis until all the tools have the same spacing (use a dowel) from the bush.  All tools would have the same Z-offset, but different W-offsets.

Tool changes would be something like:

• X move to clear the tool
• Z+ to pull stock back in to bush (if needed)
• W+ move away from bush to clear all tools
• X move to next tool
• W- to put new tool at face of bush
• Z- feeds stock out of the bush

Even if you add a Y-axis I think having a W-axis to adjust the Z-offset make sense.  Unless you have that adjustment, you are limited to using the same style or series of toolholder that puts the cutting edge in (more or less) the same Z-location.

Very small variations in Z-location can be dealt with using a Z-offset for each tool, but larger variations will mean some of your tools will not be cutting right at the guide bushing - reducing the benefit of a Swiss arrangement.  A W-axis would solve this  - giving you much more flexibility in tool holder and tool selection.

As far as your parting tool goes, just get a different tool holder. You can get left hand or right hand, and pick from a million insert shapes that gets the tool as close to the guide bush as possible.  You might even be able to flip the holder upside-down and come at the stock from the opposite side - let gravity help clear the chips.  Just try to manage the holder orientation & LH/RH so you don't have to reverse the spindle during the cycle.

My suggestion would be to look for a parting tool holder that has different insert tip geometries available.  Get two of the same holders and use one for parting - maybe with a 5 degree lead to reduce the 'tit' - and use the other holder for partial or full-radius grooving.

I prefer screw-clamp parting/grooving tools.  The holders with inserts that just wedge-in aren't really stable for side-cutting.