CNCing a 13.5 X 42 Gap Bed lathe

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13 Aug 2009 21:46 #698 by BMG
Greetings.

I recently acquired for under $200 a 1994 chinese gear head gap bed lathe that fell off a pickup truck when it was being moved to a new building. The unit is identical to a Grizzly G4016 lathe. According to the guy I acquired it from, it was used only for facing rebuilt printing press parts. The threading leadscrew was not installed on the machine and based on an inspection appears to never have been installed.

I have been tearing it down to identify the extent of the damage. Most of the handles, the cross slide and the toolpost slide took the brunt of the force. The bolts for the cover of the gearbox also sheared off (gears are ok and so is the case). The cross slide is salvageable but I suspect the tool post slide is not. Most the axles for gears in the apron gearbox have some damage. The ways and tool rest both look unscathed.

After seeing the extent of the damaged parts on the apron gearbox and lead screws for the cross slide, I figured converting this to an CNC X Z lathe would probably cost less (mechanically) than restoring it to a usable manual machine. I am a hobbyist so this would likely occur over the coming winter (and probably spring as well).

For the X axis, I am planning on using the threading leadscrew (8TPI) and driving it with a stepper or servo. I would do the same for the Z but will have to replace the leadscrew. Fortunately, they PO cut a leadscrew with an unfinished mounting end so I will get that finished and mechanically I should be good to go. Of course, I would be using EMC to drive everthing.

If anyone can offer suggestions on this project I would be grateful.

I'll post pictures later.

Thanks

Brian

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14 Aug 2009 11:24 - 14 Aug 2009 11:26 #703 by BigJohnT
A 13x42 lathe is a pretty good chuck of iron and top heavy to boot! I have a similar lathe and have considered doing a conversion or rather a semi conversion. My plan was to make a removeable X Z plate that clamps to the main slide. I've not done enough research to say if that is good or not...

Use ball screws, they are more precise and it takes much less force to turn them.

Do the research before purchasing anything. Make sure you understand how much power you need to drive your ball screws.

Avoid cheap hobby drives. Stick with well known drives like Gecko, Mesa etc.

If your planning on using software step generation (parallel port) do the research to make sure it will work for your setup.

Get a copy of EMC up and running on a computer so you can get familiar with it.

Read the manual starting with the Getting Started Guide then the User and Integrator Manual.

Get on the #emc IRC channel and chat with other users about your plans.
www.linuxcnc.org/component/option,com_mo...rc/Itemid,8/lang,en/

Consider adding an encoder to your spindle so you can do threading.

And take everyones advice with a grain of salt as they say...

And most of all have fun doing it.

John
Last edit: 14 Aug 2009 11:26 by BigJohnT.

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17 Aug 2009 01:39 #712 by BMG
Yep, The lathes certainly has a bit of iron too it. I was barely able to get it into and out of my station wagon. All told, it weighs over 1000 lbs. As mentioned, the damage repair bill precludes me repairing it for manual purposes.

Ball Screws versus existing Leadscrew - Cost for now says leadscrew. I plan on using the leadscrew and the halfnuts to move the existing apron gearbox and cross-slide plate. Once its operational and I have more cash to play with, I can always upgrade to the ballscrew.

Research... Thats where I am at now. I am considering servos out of the box along with possibly a mesa card - sizing is certainly a concern at this point in time. I also want to put an encoder on the spindle so getting a hardware card for that as well.

I already use EMC with my gantry router and originally set it up prior to the stepconf wizard, although that wizard makes it very easy to readjust my settings and test the axes. I intend on getting the simulator running to I can play with a Lathe setup.

I have been traveling to MO too much this summer to dedicate a chunk of time into tearing down the lathe and getting thoughts for how to put it back together yet. I suspect this Fall will be more productive. I should be out in the garage this week, so I will snap several pictures.

Thanks for the input.

Brian

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17 Aug 2009 13:44 #715 by BigJohnT
A Mesa 5i20 would have enough I/O to do the job well and be able to read a high count encoder. I have an Automation Direct TRD-S2500-VD 2500 line encoder hooked up to a sudo-spindle and going into a 5i20 at the moment to get used to that part of the programing.

A short example of hooking up a spindle encoder was the result of that...
www.linuxcnc.org/docview/html//examples_spindle.html#r2

If you can tolerate the backlash from an acme lead screw for the time being then you should not have a problem. Just know upfront that you can't get all the backlash out without causing a lot of friction and that will load up your drive big time.

Pictures are great.

What part of MO? I'm in SEMO.

John

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17 Aug 2009 14:43 #716 by BMG
My travels take to to Festus and Cape Girardeau. I work with the cement plants there.

Pictures tonight

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17 Aug 2009 15:42 #717 by BigJohnT
That's pretty close to me in Poplar Bluff :)

John

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18 Aug 2009 01:53 #719 by BMG
Closest I got to Poplar Bluff was on night sleeping in Sikeston at the Drury after a redeye into Memphis and a second night having some Throwd Rolls.

Perhaps I can view your machines next time I am in Cape (and have an evening to break away).

http://imagebin.ca/view/EQ6bVDw.html is a picture of the lathe. I started tearing it down a few weks back. Lots of grime and goo to scrape off.


I plan on making a replacement shaft to traverse the gearbox (line "A")
http://www.grizzly.com/products/G4016/parts/8 Case
http://www.grizzly.com/products/G4016/parts/9 Shafts and gears
That line is currently fitted with two shafts installed end to end. In the picture of my lathe, the gearbox case can be seen in front of the lathe with red paint on it.

I would then use the stripped out Apron Case
http://www.grizzly.com/products/g4016/parts
With just the Half Nut parts installed to drive the cross slide.

When funds and knowledge improve, I can swap out the leadscrew for a ball screw and modify/replace the cross-slide/apron assembly.

Brian

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20 Aug 2009 14:06 #735 by BigJohnT
Sounds like a fun project. Looks like your lathe is similar in size to mine.

i47.photobucket.com/albums/f163/johnplct...%20Shop/HPIM2631.jpg

Just thinking out loud the Z doesn't have to move very fast when cutting so with some gear reduction I wonder what size stepper or servo would do the job??? It would be nice to have at least 25 IPM for rapid on the Z...

John

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21 Aug 2009 15:33 #737 by BMG
Your model lathe in the Grizzly lineup appear to be one of the "precision" toolroom lathes. I reckon there are a few more bells and whistles on your. I also note yours is a V bed for the ways. On mine, there are two parrallel ways. I don't know the significance between the two of them, but the V version must be better since its on the costlier unit.

Once I get things completely torn down, cleaned up and reassemble the parts I am keeping, I will then figure out the electronic needs.

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22 Aug 2009 12:14 #740 by BigJohnT
Mine closely resembles this one at Grizz

www.grizzly.com/products/14-x-40-High-Pr...ool-Room-Lathe/G9732

Mine is a bit heavier and has a larger chuck mount... and is a lot older :)

John

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