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Davek0974
13-11-2018, 03:33 PM
I have a Bridgeport manual mill which i converted to CNC with servos, CSMIO control etc and ball-screws on the axes.

I now have a really nice lower half of a CNC with good positioning accuracy and the large table i like plus lots of easy access and so on.

The downside is the spindle/head - this is poor TBH and rattles (dog clutches gone) plus there is a vibration (maybe a bowed spindle spline but runs true at bottom.) The spindle is a QC/BT30 with drawbar.

The knee is currently my B axis and is coded in Mach3 to take tool length compensation.

My question is this - is it practical to rip the whole head off from the swivel ring on the base column upwards, bin it, and build a proper CNC Z axis to bolt on in its place?

I am thinking maybe a steel plate weldment with HiWin rails, servo motor plus an ATC cartridge spindle - this would remove the wobbly/weak knuckle joint and give a decent Z travel which the BP lacks badly in, it will also remove the Quill, splines, clutch and so on from the drive.

I currently have a large 3Hp AC motor on her, running 1:1 toothed belt under VFD/program control but that only gives me 4000rpm so would like some more. Maybe fit a 3kw (or more) AC servo drive.

I can't fit a "proper" cnc in due to a low roof and low power(home shop business) so looking to mod the old girl if it was a viable proposition.

Any tips much appreciated as always.

Thanks

Dave

m_c
13-11-2018, 06:25 PM
Most things are doable given enough time and money.

My biggest concern with swapping that much cast with steel, would be resonance, however given the multiple tilts/swivels/nuts/bolts that already exist between the base and head, it will probably be an improvement.

Davek0974
13-11-2018, 06:34 PM
Yes, if needed it could be resin filled in the riser section maybe?.

Its a crap-shoot i guess - was thinking 12mm plate, welded into box style weldments - big one for the swivel connector and riser section finishing in a vertical plate for the Z slide carriages. Then a box style extender starting with the Z rails and then motor/spindle cartridge.

I guess it will need a medium/high pre-load rail set to ensure no slack in Z axes, good quality stuff and a decent screw to lift it all, maybe counterbalanced as well??

m_c
13-11-2018, 06:59 PM
I would of thought a ribbed design would be better for the main section. That way you could get a reasonably nice L/Boomerang type shape going from the main body up to the vertical surface for the rails.

I could be wrong, but I have something in my mind telling me U-shapes are just about as good as an enclosed box section, but it's not really something I know that much about.

I think given the size and potential cost of the project, I'd be spending some time drawing things up in 3D software and running some FEA to see what works/doesn't work. A counter balance might be a reasonable idea, but a couple gas struts would probably be enough and reduce complexity. A quick google shows struts are available with up to 2500N (~250KG) force for not that much money (14mm rod with 500mm of stroke is available for 40+VAT from - https://gasstruts.metrol.com/fixed-force-gas-struts/fixed-force-gas-struts/fixed-force-gas-strut-f-sd04.html )

swarf-boy
20-11-2018, 09:14 AM
Just to throw you a slight curve ball,

I have a manual series 1 that I fully stripped and rebuilt a few years back, so I an very familiar with it.

I recently purchased a series 1 interact.
The head and 90 bend casting, bolt onto a std serues 1 column, with rhe usual 4 bolts ( and 2 dowls).

If you can find one, it should go straight on. And they are usually QC 30 too��.

They are a variation of the vari speed head, but most people (my self included at some point) pull out the vari pulleys and fit timming pulleys. ( usually 2:1 ratio unless you alsways want increased high speed. Possibly uprate bearings too) and speed control via VFD, controlled by CSMIO ( as you probabky already do.


Also, fit the auto oiler too, id you go this kind of direction.

Davek0974
20-11-2018, 07:02 PM
Thanks, thats an interesting thought. Not sure it will get me where i want to be fully though as the head still uses a quill so has the usual splines etc and no option of an ATC IIRC?

swarf-boy
20-11-2018, 08:02 PM
Ok 1 more thought....
The 90 bend casting has a flat verticall face.
This woumd make a good solid mount for anyrhing you could bolt to it. And if it's from a scrapper, it will be one if the few parts that could not be worn.
A much more solid option than the ram and knuck joint affair.
( but then you loose the tilt option if course)

Davek0974
20-11-2018, 09:03 PM
That sounds good, i've been trying to find a picture of the part in question but not got one yet.

I need the vertical face to be way back where the front of the round column/body is in order to get a decent linear rail system in as well as a motor and a spindle cartridge.

swarf-boy
22-11-2018, 10:28 PM
The vertical face comes forward by 32cm from the top round part of the column.

Davek0974
23-11-2018, 08:35 AM
Ok, thanks.

Its way too far out for my plan to work on that, good idea though.