Author Topic: Electronic Leadscrew for the New Lathe  (Read 51773 times)

Offline Country Bubba

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Re: Electronic Leadscrew?
« Reply #25 on: March 28, 2015, 09:04:17 AM »
It has 3 usb  ports.

But I for one, don't want a mouse in the shop.
Art
Country Bubba

Offline mattinker

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Re: Electronic Leadscrew?
« Reply #26 on: March 28, 2015, 09:11:04 AM »
Somebody needs to come out with a 5 volt single board computer the size of a credit card that runs DOS natively and has a CNC compatible parallel port and a B/W LCD display capability. Doesn't even have to be more than 100 Mhz  and look like a 486.

Or better yet, we need a DOS tablet, with a parallel port!  :lol:

Hey Steve, how about this box for dos?

http://www.roboard.com/ncbox-189.html

And it can be found here:

http://www.robotshop.com/en/roboard-ncbox-189-cnc-machine-controller.html

And their located in your part of the world!

Robotshop inc.
555 VT Route 78 suite 367
Swanton, Vermont, USA, 05488

No mouse terminal ?

John,

One problem, Steve doesn't want to spend more than two shillings and four p'nce on it!

Matthew

Offline John Stevenson

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Re: Electronic Leadscrew?
« Reply #27 on: March 28, 2015, 10:39:16 AM »
It has 3 usb  ports.

But I for one, don't want a mouse in the shop.

Der, slaps head with big dirty hand.
I have an old DOS machine running AHHA and can run that without a mouse fine but it's next to impossible to run windows programs without a mouse.
John Stevenson

Offline vtsteam

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Re: Electronic Leadscrew?
« Reply #28 on: March 28, 2015, 01:19:49 PM »
When all is said and done and we get a small computer board and a screen and a keyboard and lets say we're going to run DOS and TurboCNC....... seems like some old funky 486 DX66 laptop with a small screen and therefore a small footprint is actually going to be more compact than all the other separate micro stuff hooked together with a power supply and cables, etc.

And I don't know why I hadn't thought of it, but I do have an old Win95 NEC 486 DX66 laptop, that will run DOS on startup, actually in quite good condition stuffed away somewhere "in case I ever found a use for it".

The only question is, John S. Is TurboCNC single pulse pickup threading no good, or probably okay for a bodger like me?



ps There's a business in Vermont???
I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Electronic Leadscrew?
« Reply #29 on: March 28, 2015, 01:31:00 PM »
Pekka re. thread follower -- I really do have a soft spot in me heart for a purely mechanical solution (other than change gears) -- and I've been hanging onto this picture, got from -- I don't remember where -- for a decade.

I'm really tempted to do something like this, or along this principal, anyway. Decisions, decisions......





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Steve
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Offline Arbalist

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Re: Electronic Leadscrew?
« Reply #30 on: March 28, 2015, 02:16:24 PM »
When you think about it, it's surprising someone hasn't come up with some kind of swappable lead screw system. Not as elegant as change wheels but could be much quicker to set up?

Offline sparky961

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Re: Electronic Leadscrew?
« Reply #31 on: March 28, 2015, 02:21:25 PM »
... I do have an old Win95 NEC 486 DX66 laptop, that will run DOS on startup, actually in quite good condition stuffed away somewhere "in case I ever found a use for it"...

Old laptops that are too slow to use modern software find a perfect place in hobby CNC if you use old software or something of your own creation.  They are compact and more powerful than most people give them credit for.

The only issue I've come across in my own experience is that the processor speed can limit your maximum stepping rate.  There may be a way to get around this, but just another factor to keep in mind while you're exploring options.  It was definitely better when using "good old" DOS and TurboCNC rather than Mach3 and Windows 98.  The multitasking (task switching) nature of Windoze is the core of the problem when you're trying to do something that requires real time operation.

I never had much luck getting EMC running well on any computer.  Unfortunately my experience with other open source linux-based software seems to follow the same pattern.

Offline vtsteam

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Re: Electronic Leadscrew?
« Reply #32 on: March 28, 2015, 04:12:31 PM »
Arbalist, I was thinking similar to those lines, but  a normal leadscrew with half-nut and a second parallel pushrod to the apron -- attached there with a clamping block.

Pushrod goes back through the lower front headstock area (similar to the leadscrew) to the thread pickup arm, which rides on the spindle master screw -- similar to above pics. All the connections on the pushrod are adjustable, also similar to pic above.

You can still use the conventional leadscrew, but for threading you open the half nut and clamp the pushrod to the apron. It then controls the carriage.

In other news:

The NEC lappy is a Pent 1 it turns out, but the HD seems to be missing (did I do that?) It boots to BIOS, but the floppy drive is defunct. The HD socket connector seems to be proprietary, so I can't just drop in one of my old lappy HDs. Probably a lost cause. Too bad.

Mechanical solution is looking kinda attractive at this point unless someone comes up with a cheap simple electronic leadscrew controller board. Still open to ideas there.....

I love it when a Plan B comes together!
Steve
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Offline PekkaNF

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Re: Electronic Leadscrew?
« Reply #33 on: March 28, 2015, 05:11:15 PM »
I was about to play with velocity-tracking AC-inverter, but lost momenum...I have few 100/200W and 400W AC drives that do all sort of tricks and I think I guestimated that chucking even unmached pair of AC motors and invertters together would produce me near perfect feeds.

But there is a guy 20km away that could not stop there but used servocontroller to drive lead screw in velovity mode. If I remmber correctly he had to use eventtualy some sort of panel for user controller, but no PC, no progam licences, no mouse, no keyboard......all the smarts were on servo drive. This might or might not fit to your budget.

I like that tread follower idea too, it's all mechanical, simple, easy to understand and there will be no cheap caps to blow up their tops. I would design it at the back of the machine and normally the threads would be made away from the spindle....at great speed.

This should give you a push:
http://www.lathes.co.uk/carstens/
http://www.lathes.co.uk/stedall/
http://www.lathes.co.uk/accuratool/

just look her curves:
http://www.lathes.co.uk/accuratool/img2.jpg
That is one interesting design, but it has the horrors. But it brings your arm out of harms way.

Pekka

Offline Fergus OMore

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Re: Electronic Leadscrew?
« Reply #34 on: March 28, 2015, 07:52:51 PM »
Not wishing to wander too far off but others have mentioned simplified screwcutting gear boxes.  I had one!
I made it up to the design of Martin Cleeve which appeared in ME in the 1950's

Somewhere are the drawings but it is shown in his Screwcutting in the Lathe book. It covered what he needed to cut Imperial threads and whilst I have a full Myford box and a metric conversion, I recall his comments about 'tieing up' gears. I recall him saying that Prof Chaddock had calculated that 20 change gears could be arranged to cut 750 thousand pitches- if they were not locked in a box.

Not for me to try- counting the odd sheep is enough for me.

Good night

Norman


Offline Country Bubba

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Re: Electronic Leadscrew?
« Reply #35 on: March 28, 2015, 08:48:02 PM »
When all is said and done and we get a small computer board and a screen and a keyboard and lets say we're going to run DOS and TurboCNC....... seems like some old funky 486 DX66 laptop with a small screen and therefore a small footprint is actually going to be more compact than all the other separate micro stuff hooked together with a power supply and cables, etc.

And I don't know why I hadn't thought of it, but I do have an old Win95 NEC 486 DX66 laptop, that will run DOS on startup, actually in quite good condition stuffed away somewhere "in case I ever found a use for it".

The only question is, John S. Is TurboCNC single pulse pickup threading no good, or probably okay for a bodger like me?



ps There's a business in Vermont???

Steve,
Look at the Dakeng web site and the piece that Dave K is making for a sonar part (video at http://www.dakeng.com/TurboCNC_four_tools_turning.AVI)

Yep, turbocnc ain't dead yet!

Art
Country Bubba

Offline vtsteam

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Re: Electronic Leadscrew?
« Reply #36 on: March 28, 2015, 11:05:55 PM »
Thanks Pekka, that was interesting reading.  :beer:

Norman, yes I guess a QC gearbox could be made. There was an article in May 16 1980 ME by S.H. Abigail for a really simple conversion from loose change gears that I saved and looked at for quite awhile -- thinking of doing something similar for the Craftsman 12x36. But I never did. I should still keep it in mind. But I'd have to make up a full set of gears for the new lathe, which means making up a dividing rig, etc. I suppose one way of simple dividing would be to use the set of change gears from the Craftsman to index a cutter to make the new gears with.

Bubba, I have a fondness for TurboCad, and I actually still use it on the hot wire foam cutter.  That video is cool, but it was running so fast I finally realized when I looked at the swarf that he was cutting plastic, not steel. I've used LinuxCNC on my router. Both of these are in my big shop, where there is more room for a computer and other necessary gear.

One more thought re. electronic leadscrew and a micro single board computer running the GRBL CNC program:

GRBL does not do threading -- no input for pulse or encoder

But it does do conventional axis stepping. What if you could temporarily disengage the normal spindle motor by loosening the belt, and have another sheave with a timing belt to a stepper. Then you could just treat the spindle as just another machine axis, and since thread cutting speeds are likely to be low, and reduction to the stepper can be a reasonable amount, seems like you could just sync the spindle and leadscrew that way. Then cutting and multiple passes are all doable depending on how you write your G-code.

Similar idea I've already seen where both the spindle and leadscrew are servos, but a stepper version....



I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline Fergus OMore

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Re: Electronic Leadscrew?
« Reply #37 on: March 29, 2015, 03:18:48 AM »
Yes, but the late and much lamented Cleeve only utilised enough cogs to make the necessary threads.  I've got a heap of cogs tied up and have never been used and will never be used-- and this is a 'sight glass' Myford Super7B that Hiram Abiff made the brass pillars for Solomon's Temple( or very nearly) .Again, I've a heap of cogs for the time that I might rip it all out and fit a longer leadscrew. If I ever get everlasting life!

Seriously, apart from cutting a 1/2" BSW thread or a fine feed, that is about it. I only cut 16TPI because I'm not strong enough now  to to manually tap.

Writing as retired bean counter, having a Myford box is a better investment than having my hard earned brass in the bank.

But enough of the Ancient dis-Order of Myford Investers? What about the old Pools Major lathe? I had one- sadly worn out and past its best but it had TWO leadscrews! It simply tightened or slackened the screws for the cogs to engage or disengage. Mine had flat belts and was often archaic but these nice little touches were winners.

Electronic lathes or whatever? No, they will come for the model maker and be affordable but not in my time. Meantime, others will spend a lot of time  and money in development( and often failure).

Maybe you should make a Hozapffel with your initials cast in the legs and  a wardrobe full of homemade tools!

My kind regards

Norman

Offline philf

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Re: Electronic Leadscrew?
« Reply #38 on: March 29, 2015, 03:45:17 AM »

But it does do conventional axis stepping. What if you could temporarily disengage the normal spindle motor by loosening the belt, and have another sheave with a timing belt to a stepper. Then you could just treat the spindle as just another machine axis, and since thread cutting speeds are likely to be low, and reduction to the stepper can be a reasonable amount, seems like you could just sync the spindle and leadscrew that way. Then cutting and multiple passes are all doable depending on how you write your G-code.

Similar idea I've already seen where both the spindle and leadscrew are servos, but a stepper version....

Good idea Steve,

You'd need a fairly powerful stepper to drive the spindle and/or a big (compound?) reduction ratio to provide enough torque for coarse threading.

Phil.
Phil Fern
Location: Marple, Cheshire

Offline RussellT

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Re: Electronic Leadscrew?
« Reply #39 on: March 29, 2015, 06:19:30 AM »
Hi Steve

Having read all the responses it seems it's possible to do it electronically but it's not straightforward or it's expensive.

Constructing a quick change gearbox seems like a lot of work too.

I bought a gearbox for my lathe because I didn't like changing the wheels to switch from threadcutting to fine feed - which is one of the reasons you mention and I'd find myself trying to avoid threading because of it.

If you're building a lathe from scratch then perhaps the easiest solution would be to have two lead screws - or two gear trains - one for fine feed and one for threading and rely on changewheels for setting the thread.  Maybe you could even use the Craftsman change wheels.

Russell

Offline PekkaNF

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Re: Electronic Leadscrew?
« Reply #40 on: March 29, 2015, 07:50:38 AM »
I find the two leadscrew or one leadcref for threading and one splined shaft for feeds approach a little cumbersome.

I have been thinkking one leascrew and simple gearbox (reduced set of threads) or standard change gear arragement at spindle end and athe tail stock end coupling, gear and electric motor only for feeds. Bit like Hardinge, but much simplified.
 http://www.lathes.co.uk/hardinge/index.html

I have one little French made junk that has permananetly connected leadscrew on apron. No split nut. It is a little annoying to use but most of the time not as much as you might think. It got me thinkking if I could get away with rotating nut on the apron. I.E:
* threading per changegear (it has plastic change gears)
* Manual feed at the end of the leadscrew....there is a dog coupling to disengage threading/feed.
* electric motor to rotate the nut on the apron for variable speed feed.

Only downer is that to move the saddle from one end of the machine to the other would take a lot of crankking.

Myford 10 has very interesting arragement
http://www.lathes.co.uk/myfordml10/

There is very basic changegear arragement for threading/feeds that is straight connected to leadcrew.
On apron there is no halfnut, but a helical gear meshing with leadscrew. The gear can be turned with handwheel. Downside is that handwheel turns when leadcrew turns and saddle is stationary

But here is the idea: What about having a coupling (or gear) that will alternatively mesh with handwheel or electric motor?

The big idea:
1) Leadcrew is rotated only for threading and it has whatever gear set you need or forgot there. To thread you need to mesh gears on banjo and  gear on apron is stationary (worm gear on electric motor or halfnuts).
2) Leadscrew is moved out of mesh, stays stationary and is used as a gear rack. For all other uses than threading. Myford 10 has crank at the end of the leadcrew for hand cranking (inching, halfnuts coupled), but you have to drive all selected change gear cluster.
3) Automatic feed with an electric motor, at the end of the leadcrew(=need coupling) or at the apron, needs coupling too.
4) Manual feeds with granking on apron, halfnuts disconnected and possibly.

Then again maching small gear rack and pinion is not too expensive here, but one more arragement to lined up an to be fitted.


Feeds, even spindle speed coupled is very easy to make with electric motor.

Threading looks very simple on ELS-principle, but there are very narow margins, unless 1 or 2 axis CNC approach is fully accepted. Then it is not anymore very cheap and simple.

I am electrical engineer (control systems) and my choice for threading would be between change gears and/or greatly simplified crew cutting gearbox. And electric feeds.

Sounds like VT:s choice is between CNC and thread cardride/follower. Two really different animals! I'm really intered to see which way is taken. I think that follower would be very beautiful and it screams cast parts. CNC approaches often seems to come out untidy. Not pretty.

Pekka

Offline S. Heslop

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Re: Electronic Leadscrew?
« Reply #41 on: March 29, 2015, 09:28:05 AM »
I'm no lathe expert but looking at them it seems that it's quite common for there to be a leadscrew with a spline in it, that works as a leadscrew and an autofeed thing. You could probably do some sort of worm gear thing with that, maybe all attached to some sort of pivoting block that rotates a gear meshing with the pinion down and out of the way. I was looking at those popular youtube videos of people hobbing worm gears on the lathe with regular old taps and it seemed pretty viable to me (but probably has alot of backlash). It's something I want to try out for making guitar tuners at some point.

Offline vtsteam

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Re: Electronic Leadscrew?
« Reply #42 on: March 29, 2015, 09:32:33 AM »
Norman, Phil, Russell, Pekka, thank you for your thoughts here -- it really makes this interesting and helps greatly in weighing the options.  :thumbup:

STEPPER:

Phil I wonder how big a threading stepper and reduction on the spindle I'd need to cut, as a practical maximum let's say an 8 tpi Acme thread on say 1" dia mild steel rod.

Would a 270 oz-in stepper motor handle it with say a 4 to 1 reduction? (The spindle is roller bearing supported, and the leadscrew would be separately driven, so, not a load in this case.)

CHASE THREADING:

I see lathes UK calls the master screw and followers "chase threading". Must have evolved from the hand chaser and Tee rest method.

I'm still kind of attracted to this one because of its wonderful simplicity. I would definitely drive the apron in front, though, and run a pushrod parallel to the leadscrew, unlike any of those I've seen so far.

I would likely put the master screw on its own idler spindle with timing pulley -- close to the pushrod bearing, on the gear side of the headstock -- and run a belt to the spindle. This would reduce the length of the pickup arm and allow a change of simple pulley ratio between spindle and master screw. That last would reduce the number of master screws and follower nuts needed for a good range of threads. Pratt and Whitney did this, I think with master screws of 5, 5.5, 6, 6.5, 7, 8, etc.

It would also utilize the carriage and ways guidance for the cutter, rather than requiring the heavy rod on the rear of the lathe as a guide. The front mounted apron pushrod would no longer need to be of heavy proportions of the old style chase threader attachment. To me, the old style needed beef because they were acting effectively as an auxiliary cylindrical ways, supporting their own toolpost. It might be argued that the rear toolpost was a benefit, but that can also be achived on the conventional carriage -- as is done for an auxiliary parting toolpost these days. I was already planning on that anyway.

CHANGEWHEELS/GEARBOX:

Still a possibility. I think the things I hate most about the Craftsman could maybe be tamed somewhat in a new lathe. The blackened oily gears, heavy floppy three slot banjo, indecipherable gear chart and awkward insert system with conventional bolts could probably be better thought out.

I guess one benefit of plastic gears is no oil needed. Maybe timing belts could replace some of the gearing. Or the gears run for threading only without oil somehow. Simple things like an internal light and custom made gearing wall chart would make sense -- and probably everyone else is smart enough to already have that. What about a quickly removable gear frame, so you could lay most of the train out on top of the workbench while changing gears around?

I could use the Craftsman gears on the new lathe, and with these changes make the operation more tolerable.

Also, feeds could be handled the same way many of us add feeds to a mill -- a DC motor and speed controller -- detach changing feeds from the need for gear changes in threading. That could be done through two leadscrews, or one with a simple dog clutch and engagement lever for the motor (as done on mill tables to allow manual use).

Okay so if I did something like an adjustable  DC motor drive for feeds, and a removavble "frame of gears" for threading. The frame could be stored out of the lathe normally, and just popped in when threading was needed. Easy to work on, easy to keep clean, and set already to the last thread cut -- no need to revert to a feed ratio. That doesn't sound too bad....
« Last Edit: March 29, 2015, 10:03:25 AM by vtsteam »
I love it when a Plan B comes together!
Steve
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Offline philf

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Re: Electronic Leadscrew?
« Reply #43 on: March 29, 2015, 10:19:17 AM »

STEPPER:

Phil I wonder how big a threading stepper and reduction on the spindle I'd need to cut, as a practical maximum let's say an 8 tpi Acme thread on say 1" dia mild steel rod.

Would a 270 oz-in stepper motor handle it with say a 4 to 1 reduction? (The spindle is roller bearing supported, and the leadscrew would be separately driven, so, not a load in this case.)


Steve,

As has already been pointed out 270 oz-in will be the holding torque and as soon as you try to bring speed into the equation the torque will fall off. The reduction between stepper and spindle will increase the torque proportionately but at the expense of max speed. Speed doesn't seem to be an issue for screwcutting as many users advocate hand cranking the spindle which probaly means you'd be 60 rpm maximum. If I were doing this I'd try a more powerful stepper (my CNC mill uses Nema 23 3.1 N-m (440 oz-in) motors which are cheap enough) and a higher reduction.

What's the biggest diameter and coarsest pitch you're likely to need? A 3" diameter 8 tpi  thread will obviously require much more torque than a 1/2" 32 tpi.

Something else to think about is what will happen if the spindle stepper stalls - The control probably wouldn't know and the tool would try to plough a groove along the workpiece.

There's a lot of discussion on various forums about using stepper powered spindles but not many seem to have got beyond the talking stage. There are kits available for the tiny Sherline lathes.

Phil.
Phil Fern
Location: Marple, Cheshire

Offline Fergus OMore

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Re: Electronic Leadscrew?
« Reply #44 on: March 29, 2015, 10:58:44 AM »
Steve,
             By now you will have copies of what Martin Cleeve did to the part Myford ML7 that he purchased.

Obviously, it is all 60  year old stuff but it sort of collates a lot of original thinking.

Me, I was mulling over all this excellent information and began to realise that I had a spare Myford rack( actually 2) and wonder why no one has gone along propelling machine tool movement( model wise) with hydraulics. I was having a bit of a down with the death/funeral of an old marine engineer mate/engineering college mate/boat builder mate and lots more. I sort of think that he would have had similar thoughts .
Hope my downloads are of interest

Norman

Offline vtsteam

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Re: Electronic Leadscrew?
« Reply #45 on: March 29, 2015, 11:07:28 AM »
Phil,  :beer:

I do have some 400+ oz in steppers already, though intended for another project.  I guess I could use one for this.

re. capacity I definitely wouldn't expect to do 3" x 8 tpi on this little lathe (mini-lathe 7x12 class). More like a max threading capacity of say1" x 8 tpi acme in mild steel.

If it seems marginal even w/a 400 oz in stepper @ 4 to 1 as a threading spindle motor, then it probably isn't what I want -- something physically large with commensurate power supplies, and support space taken.

The spindle stopping issue is something to think about.
I love it when a Plan B comes together!
Steve
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Offline awemawson

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Re: Electronic Leadscrew?
« Reply #46 on: March 29, 2015, 11:09:30 AM »
Well my first NC mill was all hydraulics with Moog proportional valves, but amusingly the way that they did 'rigid tapping' was to have a feedback 'quill' follow a master thread attached to the main spindle. Any error following the thread pitch resulted in follower deflection and adding a correction factor to the hydraulic equivalent of a 'summing junction'
Andrew Mawson
East Sussex

Offline vtsteam

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Re: Electronic Leadscrew?
« Reply #47 on: March 29, 2015, 11:33:05 AM »
Norman, thanks, much to absorb........ :coffee:
I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Electronic Leadscrew?
« Reply #48 on: March 29, 2015, 11:34:55 AM »
Simon, thanks. But I don't quite understand..., sorry!  :scratch:
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Steve
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Offline Fergus OMore

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Re: Electronic Leadscrew?
« Reply #49 on: March 29, 2015, 12:39:17 PM »
Simon, thanks. But I don't quite understand..., sorry!  :scratch:

I do. This was what my Pools Major had. There was a peg in the gear- which moved the saddle etc-mine from the back. This malarkey would cut tapers. :doh:

N