Bridgeport clone quill / knee conversion

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Bridgeport clone quill / knee conversion

This topic has 9 replies, 8 voices, and was last updated 12 June 2011 at 16:25 by Jim Nolan.

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20 November 2010 at 13:03 #58990
David Colwill
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@davidcolwill19261
Hi

I have started CNCing my King Rich bridgeport. X and Y are fine but I am hovering between the quill versus knee issue. I had originally planned to do the knee by fitting a ballscrew and nut with a timing pulley mounted directly on the ballscrew and having the stepper motor underneath the table, the whole lot to be counterweighted by two gas rams. I was told that this arrangement had problems due to inertia and that working with small drills and cutters was a problem. I then started to think about doing the quill but the issue there seems to be that you can’t get the drive close enough and mounting motors etc seems problematical. Has anyone done any of this? Any thoughts?

Dave
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20 November 2010 at 13:03 #14938
David Colwill
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@davidcolwill19261
20 November 2010 at 14:39 #58992
Weldsol
Participant
@weldsol
Could you not drive the auto feed spindle ?? then you could select wether to use manual or CNC operation

Paul
20 November 2010 at 15:50 #58995
KWIL
Participant
@kwil
There was an article in Digital Machinist some time ago about powering the Quill, but the problem of their approach was that it was via the downfeed handle input shaft with all the backlash that that involved with a rack operated Quill. The same will apply to the auto feed because that also goes via the rack on the rear of the Quill. The only way around this is a direct input to the quill itself which has been done by connecting the “stop” hole on the front face of the quill to a suitable leadscrew arrangement, there have been some commercial units which do this I believe.
2 December 2010 at 06:50 #59805
Steph
Participant
@steph
Hi, I too am in the process of converting a bridgport (clone) to CNC. With regards to the quill having some kind of drive attached, most conversions seem to favour a direct connection to the front of the quill- shaft, in manual mode this has a direct attachment to the adjustable depth indcator. A similar setup is used on XYZ machine tools Protrack systems. A handwheel is also attached to he motor shaft to provide manual feed.

BTW are you using steppers or servos?

Regards Steve
5 December 2010 at 22:45 #60034
David Colwill
Participant
@davidcolwill19261
Hi Steve,

I have been looking around and I agree most commercial systems use the front of the quill. I am starting to head towards the option of motorising the knee, partly because of rigidity and partly because I like the idea of having a high speed head on the other end of the ram for occasional routing jobs. I have used steppers which seem Ok for my purposes although I will have to use gas rams to lighten the knee if I go down that route. Let me know how you are getting along and good luck!

Dave
11 June 2011 at 06:32 #70115
David Senior
Participant
@davidsenior29320
It may be a bit late to add to this thread, but I motorised the knee of my Myford VMF mill (article published in MEW issue 137). I had problems with the weight of the knee assembly, and the conversion had it’s limitations. To solve this, I added gas springs, which was very successful. I submitted 2 follow up articles to the editor but unfortunately they have never been published.

I was very pleased with the overall conversion, and it allowed me to dabble with some ideas for products to fit to my classic mini. Things moved on from there when I decided to try and sell those products, such that my company bought a ‘proper’ cnc mill. Now the VMF gets little or no use, and seems incredibly slow compared to the scary speed of a modern machine!

Let me know if any more details would be useful.

Dave
12 June 2011 at 08:38 #70159
GLENN BUNT
Participant
@glennbunt80076
Hi,

I have recently completed a CNC conversion of a Tom senior Light vertical and I decided to use the knee as the Z axis. I chose Arc Euro Nema 34 stepper 6.5 N.m motors wired in parallel configuration mounted alongside the knee and connected to the hand wheel arbour via timing pulleys and belt. I chose a 25mm dia ballscrew for the axis and used the ends of the old leadscrew to retain the straight bevel gear mechanism. I fitted two gas struts from http://www.sgs-engineering.com to even out the load on the motor. This works fine, in recent tests the axis was repeatable within .0005” and as an additional benefit the machine can still be used manually. It won’t compete with a dedicated CNC machine for speed but it was very satisfying to see 90+KG of machine rapidly traversing up and down via CNC control. I hope to submit an article later this year on the conversion.
12 June 2011 at 09:22 #70160
David Clark 13
Participant
@davidclark13
Hi Glenn

I am interested in the article.

Might be able to use the X and Y on my light vertical.

I would not bother with the Z.

Use it like a Protrack mill, I did a lot of useful work on one of them with just the X and Y and you could still use it as a manual mill.

It opens possibilities.

regards David
12 June 2011 at 16:25 #70191
Jim Nolan
Participant
@jimnolan76764
David,

You might want to Google Bridgeport knee CNC conversion or something like. In the last month I have stumbled across a pretty comprehensive guide to the knee conversion. There was a load of photographs and detail on how it was done. Don’t know where it was might have been CNC zone but I cannot remember.

Jim
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