Bridgeport Manual to CNC conversion...

[Davek0974]

Control options...

Not sure we need a alpha keyboard for a mill, hows about a touch-screen monitor to do away with the mouse and a small numeric USB keypad?

Or

normal monitor (cheaper/stronger) and a track-ball and numeric keypad?

Looking at controls..
X/Y joystick
Z joystick
Knee up/down buttons
Speed override knob
Feed override knob
Cycle start
Feed-hold
Stop


Spindle motor...
This is currently run from a VFD but only at 50Hz, the head is the vari-speed unit with back-gear so i have 50-3000rpm but in two ranges and manual speed control. Whats a good option here - using the VFD won't address the variable torque ability of the vari-speed unit so can't just lock it in one spot.

Any cool options here to play with?

With a bit of fiddling the vari-speed changer could probably be motorised with a stepper and gearbox, not sure it's worth it?

Mach can obviously take over the Fwd/Rev function - still using the old switch but I wired it to the VFD so I can plug-reverse for tapping;) That was before i got the tapping head.

Any cool ideas?

[Davek0974]

Z axis...

It looks like I have four options here...

1 - Drive the Quill direct from the bolt point where the depth gauge mounts at the front.
2 - Drive the manual lever shaft on the right side
3 - Drive the power-feed clutch shaft on the left side
4 - Drive the knee lift

Points -
Option 1 seems to be the most common but adds a lot of bulk to the front of the head and costs a little Z axis travel.

Options 2 & 3 are similar, both will suffer from the rack backlash but option 3 is the neatest one, backlash can be reduced with the clock-spring.

Option 4 is a contender I think, it gives a massive 300mm Z travel, but suffers from stickiness and has backlash in the bevel gears. The force is reasonable - I measured my one and if my figures are correct, it needs approx 1Nm to lift the knee based on the handle length of 160mm and 6kg force on that handle 6kg / (1000/160) = 0.96Nm

The backlash is a factor but the Z is usually used to plunge or position - both of these are done in the positive direction so maybe backlash does not matter here?

Thoughts?

[Davek0974]

Based on advice, 750w AC servos and 2:1 is ideal on a bridgeport so that is whats going in, totally overkill for the Z axis but the price of smaller motors is higher so i cant see the point really, keep it all the same.

Got a few parts on the way - stainless panel mount keyboard, stainless panel mount trackball, some bits from the box at work - nice 10-turn pots and dials for FRO & SPO controls, a few spare relays and other bits and bobs.

Just about got a source lined up for a ballscrew kit - this bit really hurts the wallet :(

Does anyone have a drawing or sketch that would give me the dimensions of the right table (X) bearing bracket and the front (Y) bearing plate??

Mine will be missing as I have the original 6F power-feeds which will be taken off when i convert.

I can get the parts but the prices seem silly and they surely must be an easy enough part to make up from steel or aluminium?

Thanks

[Davek0974]

Drive belts - HTD5mm x 15mm wide big enough?

[JAZZCNC]

Drive belts - HTD5mm x 15mm wide big enough?

They'll work ok but i'd be more inclined to go with 25mm for Mill with heavy bed.

[Davek0974]

They'll work ok but i'd be more inclined to go with 25mm for Mill with heavy bed.

Hmm, will have to check pulley dimensions will fit machining on shafts, there is a conversion kit which uses 1/2" belts, I thought that was a little weak so went for the 15mm size as i used before.

Will look into the 25mm size

[Davek0974]

Drive belts, just had a chat with a very knowledgeable guy and it seems HTD is the best option here, GT is better but more expensive all round. The backlash concern is valid but equates to approx 0.25mm linear which if i have my sums right on 5mm pitch screws and a 75mm pulley will give me an error of 0.0053mm - I think thats acceptable on a 30+ year old machine ;)


He did however strongly recommend going for 8mm pitch and 20-30mm wide belts.

Can't use 8mm pitch as you can't get the needed ratio in as the pulleys are so much bigger so will have to be 5mm pitch.