Weiss WMD30LV conversion project

[LongRat]

Here's the trickiest part to design, the X screw and nut installation. I was hoping to use a 20mm ballscrew here but that almost certainly isn't going to fit. As always, it is the issue of the bottom of the table hitting the ball nut. Here are the dimensions as seen on the stock machine with the bearing block removed.



I'm not keen to remove material from the underside of the table. If nothing else, I don't think it is all that thick so I would rather leave it. Pretty sure I will put a 16mm screw and nut here.

[HimyKabibble]

If you use a flanged 20mm ballnut, like the ones sold by HomeShopCNC.com, and recess the nut into the base, so the screw sits just above the top of the base, it looks to me like it would fit, worst case by removing just 1-2mm from the underside of the table or the top of the base.

Regards,
Ray L.

[John S.]

Can't see a problem with a 16mm screw on this size machine, a lot of the US guys use the standard Nook 5/8" screws when doing Bridgeport conversions.

John S.

[HimyKabibble]

Originally Posted by John S. Can't see a problem with a 16mm screw on this size machine, a lot of the US guys use the standard Nook 5/8" screws when doing Bridgeport conversions. John S.

5/8" is WAY small for a BP. I used 1" Nook XPRs on mine, and there's still measurable "wind-up" on the screws. I can't imagine how bad 5/8" would be.

Screws are available in 5/8", 3/4", and 1", 16mm, 20mm, and 24mm. I'd use the biggest screw that could possibly fit.

Regards,
Ray L.

[LongRat]

Ray, I agree with the concept of using the largest possible screw. That was my intention, but the 20mm ballnut will not fit without extensive table grinding. The indicated 28mm height will only fit a 16mm flanged ballnut if 2mm is removed from the existing flat on the flange. For a 20mm flanged nut, the main body of the nut won't even get in there, much less the flanged section - and that is after moving the screw down until it almost touches the saddle.
If I had a large mill on which to remove some material from the saddle I would consider that, but I don't want to hack at it manually.
I think the 16mm screw will do a good enough job on this machine in any case. If I really found the need for a larger screw, rather than mod the table with a grinder I would be tempted to fit X axis linear guides which would also increase the height available for mounting a nut.

[ihavenofish]

16mm should be adequate and long as you dont use agressive accelerations.

im not sure what you can fit in there though.

a "standard" slim nut on a 16mm screw is 40mm tall. 20mm to centre, plus 8mm for half the screw. so 28mm from the top of the flange to the bottom of the screw. youd need to cut a channel about 2mm deep into the saddle or table to fit.

the same tyle of nut in 20mm needs 32mm clearance, so youd need a 6mm deep channel, which might be pushing it.

other screw mounting types might have more clearance, but the ones ive found seem to be either very expensive or lacking in precision/anti-backlash properties.

im anxious to see what you arrive at though as im probably getting this same machine in the near future.

[HimyKabibble]

Originally Posted by LongRat Ray, I agree with the concept of using the largest possible screw. That was my intention, but the 20mm ballnut will not fit without extensive table grinding. The indicated 28mm height will only fit a 16mm flanged ballnut if 2mm is removed from the existing flat on the flange. For a 20mm flanged nut, the main body of the nut won't even get in there, much less the flanged section - and that is after moving the screw down until it almost touches the saddle. If I had a large mill on which to remove some material from the saddle I would consider that, but I don't want to hack at it manually. I think the 16mm screw will do a good enough job on this machine in any case. If I really found the need for a larger screw, rather than mod the table with a grinder I would be tempted to fit X axis linear guides which would also increase the height available for mounting a nut.

I don't think you bothered to look at the 20mm nuts I recommended, they should fit easily without grinding the table much, if at all. They are 36mm across the narrow part of the flange. If set into the base so the screw is just above the base, the height would be barely over 28mm above the base. Like I said, you'd only have to remove 1-2mm at most, and you should easily be able to take that off the top part of the flange.

Regards,
Ray L.

[ihavenofish]

Originally Posted by HimyKabibble I don't think you bothered to look at the 20mm nuts I recommended, they should fit easily without grinding the table much, if at all. They are 36mm across the narrow part of the flange. If set into the base so the screw is just above the base, the height would be barely over 28mm above the base. Like I said, you'd only have to remove 1-2mm at most, and you should easily be able to take that off the top part of the flange. Regards, Ray L.

yup, the 20mm one on homeshopcnc would fit in the same space as a 16mm "standard" nut. prices on that site are very high and the screws are c7 though, so id try to find something better in the same format.

theres a fellow on this board in canada selling c5 and c3 screws. ill ask him for dimensions.

[LongRat]

Ray,
I did look at the HomeshopCNC screws you mentioned. In fact I have some from them on my current machine. The cylindrical section is dia 30mm. That can not fit, without cutting the table or the saddle which I don't want to do. I am pretty sure that grinding that portion of the nut is not a good idea, but the flange is fair game.
Ihavenofish - C7 is good enough for what I want to do. And although the Homeshopcnc stuff is decent quality I am sure, their prices have risen a huge amount since my previous order from them. I would be interested to hear about the C5 and C3 screws all the same.

[Hans_G]

You might look at ISEL products. Their type 1 anti-backlash nut for 16mm screws is 25.3mm tall (available in 4 & 5mm lead), see http://www.techno-isel.com/LMC/Products/BmNuts16a.htm. Price looks similar to homeshopcnc, but ISEL doesn't claim "superior straightness" like hopeshopcnc does. It's funny because I'm serious.

[ihavenofish]

Originally Posted by Hans_G You might look at ISEL products. Their type 1 anti-backlash nut for 16mm screws is 25.3mm tall (available in 4 & 5mm lead), see http://www.techno-isel.com/LMC/Products/BmNuts16a.htm. Price looks similar to homeshopcnc, but ISEL doesn't claim "superior straightness" like hopeshopcnc does. It's funny because I'm serious.

.1mm/300mm. thats .004" per foot lead error. thats c10 grade. c7 is .0018" per foot. c5 is .0008" per foot.

with nearly 2 feet of x travel, i dont know if those isel screws are good for a mill, particularly when better ones can be found much cheaper. theres no issue fitting 16mm screws in as it is - just needs a small recess in the saddle for the flange. its 20mm that he wants to try and squeeze in.

[Hans_G]

Originally Posted by ihavenofish .1mm/300mm. thats .004" per foot lead error. thats c10 grade. c7 is .0018" per foot. c5 is .0008" per foot. with nearly 2 feet of x travel, i dont know if those isel screws are good for a mill, particularly when better ones can be found much cheaper. theres no issue fitting 16mm screws in as it is - just needs a small recess in the saddle for the flange. its 20mm that he wants to try and squeeze in.

ok. Thanks for pointing that out. I feel a lot better now, and I'm sure you do too.