Custom Z Axis screw from scratch- what material?

[Odin]

Hi everyone.

I have an ambitious project planned to make a new Z axis column from scratch with extended travel for my Taig mill-
nearly doubling my Z axis travel, and a radical new mounting for the Taig motor that will allow multiple pulley setups
to finally get my spindle speed down to (hopefully) around 50 RPM (!) all the way up to the max 10,600 RPM.

I need low speeds, 50- 300 RPM, to do proper drilling and milling of tool steels. 1,050 RPM on my upgraded motor
doesn't come close to a safe milling or drilling speed for stuff like 303 stainless, A2, or 1018 cold rolled, which I work
with now on manual lathes at school. I'd get a variable speed motor, but the horsepower drops as speed drops, and Lane's
model only goes down to 500 or so RPM anyway.

I recently did mill some 303 stainless metric bushings and custom hex bolts on my Taig, but due to the 1,050 RPM lowest speed,
I had to go extremely slow and light on feeds. The machine should be capable of more than cuts of 0.003" with a 7/16 3 flute
roughing E/M, it just needs a much slower speed. (It did do a really nice job though at 1,050 RPM, and slow light feed)

My new design will move the motor to a very interesting place, and counterbalance my spindle. It will be a project that takes
several months at least. The new ways will be made from either A2 or O1 tool steel, and surface ground at school.

I've thought of calling Taig for the hard part- make me an extended Z axis screw, about 20" long, but then I realized I can make
one at school on a full sized engine lathe. Taig would probably charge me an arm and a leg anyway, if they could even make it.


My three questions:

1. What material would be ultimate for a one-off custom lead screw? I'm thinking O1 drill rod,
but am open to any material. For steels, I have machined 303 & 316 Stainless, 1018 cold-rolled,
A36 structural, and 4140 tool steel with success, but am open to other grades.

2. Instead of thread-formed, as stock Taig screws are, this will be single-point threaded with a
surface-ground HSS 60 degree threading tool, with no radius point. Will this design cause problems
over thread formed somehow, or compromise accuracy?

3. Should the screw be hardened, and if so, before or after cutting the threads or form? I am
worried that if I cut the thing full, and then have to harden it, it will distort enough to screw up
the fit, but if hardened before cutting, will be impossible for me to cut, depending on the material.


Any help is appreciated- when the radical design is finished, I will definitely share the design outcome
if I can get it working.

[cameraguy]

I've thought of calling Taig for the hard part- make me an extended Z axis screw, about 20" long. Taig would probably charge me an arm and a leg anyway, if they could even make it.

Why don't you try an X-axis leadscrew instead? They are identical threads and ends, and far longer than the Z screw. Exactly the same thing, just longer. Only cost a few bucks as well.

I bought a spare Z-axis screw from Taig and used it to extend my Y-axis. Not tough when its a straight swap like that, ends were turned the same and everything.

[awerby]

Even using a full-sized engine lathe with good specs, you'll be dealing with severe deflection issues on a screw that long. Eliminating them will probably take building a special custom steadyrest that will follow the toolpost and won't mar the threads. I think you'd be better off finding a screw already made, and modifying it to fit. Or, as was suggested, just using the X-axis screw, which is about 19" long, as I recall.

Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software

[daedalus0x1a4]

Most lead screws are made out of stainless but if you want to be ridiculous try 4330M or 9Ni-4Co-0.3C

[Odin]

Guys, believe me- I thought of just buying the X Axis leadscrew from the beginning.

Problem with that is, the X & Z axis screws are threaded opposite. One is left hand thread, the other is right hand thread.

Why does that matter? I'm not sure. I have this bad feeling that somehow, with the rotation of the spindle, using the X axis screw would make the machine pull the spindle down into the work or something, or make something unscrew. Anyone know if I'm right?

Has anyone used the X axis screw for the Z axis? Would the opposite threading hurt anything?

I know if I got the X axis screw, I'd have to buy an X Axis screw bushing- the one on the Z column would not thread into it, as they are threaded opposite.

I would love to just use an X axis screw, but someone needs to convince me the opposite threading wouldn't matter.

[awerby]

If you twist it the other way, it will thread into the nut. You can change the direction of rotation in software; it's a simple matter of switching the direction bit. As long as the spindle moves up when you tell it to move up, and down when you tell it to move down, the endmill won't be affected by which way the stepper motor turns in doing this.

I haven't done this myself, but I really don't see any problem with it. And finding out will be a lot easier and cheaper than trying to make a screw from scratch that actually works. Why do you need such a large Z-travel? Are you doing some operation on really tall parts? Make sure you make the column substantial enough to deal with the extra leverage the longer axis will exert. I also didn't understand what you meant by using the spindle motor as a counterbalance. Do you have a drawing of this idea?

If what you're really trying to achieve is slower RPMs, why not just set up a jack-shaft with an auxillary pulley on it? Run the smallest pulley on the motor to the largest pulley on your jack-shaft, and then the smallest pulley on the jack-shaft to the largest pulley on the spindle (this will require taking the spindle pulley off and reversing it from its normal position.)

Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software

[Odin]

Why am I doing all this? The Taig's biggest flaw in my opinion is that it has so little Z travel. I always have barely enough room for at
least one dimension in my projects. If you haven't noticed, people wanting more Z axis travel is a very common theme with these mills.

I do a lot of work with a special 4th axis setup of mine in vertical position, with a bigger 4 jaw chuck on my sherline rotary table with a
custom made adapter plate I made. That setup alone takes up about 5.5" of my available Z travel. Factor in my endmill, and I often have
little room to work with. I'm really tired of this. I wanted to use a boring head on the Taig as well- but I would never have the travel I need
if I didn't extend the Z. Forthoming projects include long bored revolver barrels. And no, I don't have the money to buy and outfit a lathe.
This mill can do it all if properly set up.

I have been planning to extend my Z axis on my own for a while, but just recently found that there was no good option to bring down
speeds to realistic ones for drilling and milling steel. I do a lot of work in 1018 and 303 stainless. I need to drill steels, and 1,050 RPM
is insanely fast for that, drills just skip. Milling takes forever, where the machine could take a lot more off if I could just run it at a proper
lower speed for my endmills.

The way the Taig is sold is more geared towards what people popularly work in- aluminum. It does aluminum wonderfully for me
with the stock speeds, and even huge 1/4" to 1/2" cuts with a good 3 flute roughing EM. But I work more in steel, and the machine has done
303 SS wonderfully for me, but I have to go ridiculously slow on feed, and very shallow cuts, due to the high min speed. The machine could
handle a lot more, but it needs a lower speed.

When I was thinking of how to lower the speed without a vari speed motor that would just lose horsepower at low speeds, I did indeed
come up with a multi-pulley setup. Mine uses 4 pulleys, but it was the design I ended up with that became perfect when this design for
extending the Z axis finally came to me. The 2 items designs reinforce each other, I can't explain it all now. The entire Z column will become
counterbalanced, though, and become one giant gib, using a bigger 3" square tube, and a modified design.

My mill is manual- the way I like it.
I have built custom computers, and was a CNC programmer and operator for a living, but I prefer manual milling at home, no stepper motors here.

[cameraguy]

The only difficulty in using a x-axis screw is simply remembering to also use a matching nut on that axis for the new thread direction. Also a cheap Taig part.

The reason Taig mills use both right and left hand thread - and the only reason - is that it was originally designed for use as a manual mill. It is simply convention for manual equipment; manual mills do that so the direction of handle rotation is intuitive, and not confusing to the person standing in front of it cranking it. That way on all mills and on all axis, regardless of how it is driven or geared, or the screw is carried or fixed, a clockwise rotation of the handle always moves the axis the same direction relative to the handle. Thats it. Simple. Some machines therefore must use one or more reverse threaded axes to accomplish this. No magic to it.

If it is for cnc, thread direction is truly irrelevant. Purpose-built cnc machines almost always use only one direction of thread on all of the axes just for simplicity, unless of course they were a conversion from a manual mill.

[Odin]

The only difficulty in using a x-axis screw is simply remembering to also use a matching nut on that axis for the new thread direction. Also a cheap Taig part.

The reason Taig mills use both right and left hand thread - and the only reason - is that it was originally designed for use as a manual mill. It is simply convention for manual equipment; manual mills do that so the direction of handle rotation is intuitive, and not confusing to the person standing in front of it cranking it. That way on all mills and on all axis, regardless of how it is driven or geared, or the screw is carried or fixed, a clockwise rotation of the handle always moves the axis the same direction relative to the handle. Thats it. Simple. Some machines therefore must use one or more reverse threaded axes to accomplish this. No magic to it.

If it is for cnc, thread direction is truly irrelevant. Purpose-built cnc machines almost always use only one direction of thread on all of the axes just for simplicity, unless of course they were a conversion from a manual mill.

Thank you- this makes sense enough to convince me.

I wonder- if I ordered an X axis screw from Taig, if they could make one 2-3" longer for a small price.... I keep thinking, I'd like to try boring a 9" pistol barrel on the mill with a lot of setup work- I just don't have room for a lathe.

If I have to settle for 18" of screw, I will.

[cameraguy]

I keep thinking, I'd like to try boring a 9" pistol barrel on the mill

You do know that the entire headstock comes off of the Z dovetail plate with one allen screw, right? Just look up the Taig part number for spare dovetail plates, they are only a couple bucks. If you get some t-nuts and clip down that extra dovetail plate on the far left end of your table, you can simply remove the headstock assembly and reattach it down there. Then it's a lathe for horizontal boring. Attach your tool posts to the Z column at that point.

Bad blurry example but it gives you the idea;
http://www.youtube.com/watch?v=2Munq_hXxTs&feature=player_embedded]Taig CNC mill/lathe - YouTube

This is pretty much what I do when I need more Z travel, except I have a spare dovetail plate so I don't have to remove the original and re-tram it everytime I move the headstock.

[freyahong]

i dont know anything about cnc machine, i just come here to learn and try to figure out in my empty brain. hope i can learn sth from here. you are all masters for me. if anyone want to teach a baby the start of machine knowledge, contact me pls. my reward can be a smile, a sincere thx. thx very much

[Odin]

I keep thinking, I'd like to try boring a 9" pistol barrel on the mill

You do know that the entire headstock comes off of the Z dovetail plate with one allen screw, right? Just look up the Taig part number for spare dovetail plates, they are only a couple bucks. If you get some t-nuts and clip down that extra dovetail plate on the far left end of your table, you can simply remove the headstock assembly and reattach it down there. Then it's a lathe for horizontal boring. Attach your tool posts to the Z column at that point.

Bad blurry example but it gives you the idea;


This is pretty much what I do when I need more Z travel, except I have a spare dovetail plate so I don't have to remove the original and re-tram it everytime I move the headstock.

Sir, you have bested me. HOLY SH*T

Yes, I know I can take the Z headstock off the dovetail with the one screw. And I've thought of using gang tooling and making the 90 degree Z axis
a vertical lathe.

But I have NEVER seen anyone setup like that- and it makes perfect sense! I cannot believe I never thought of that! You just opened an entire new
dimension of machining to me beyond my wildest dreams. I'm looking at my mill and realizing I already have a full, huge lathe sitting in front of me,
The only thing I don't have are change gears to do threading! Maybe there's a way to even do that?

I am dumbfounded. I cannot believe I never saw anyone do that before. Please, do you have any other threads or pictures of this setup?
How did you re-mount your motor?

I'm thinking still of extending my Z, but now, maybe not as much. I'm thinking in addition, of making a quick connect spindle mount to the
X ways for an extra ER-16 headstock, for instant lathe, and with 2 running spindles, live milling!

Head is exploding now