Town Woodhouse milling machine re-commission and cnc conversion

[awemawson]

When you come to replacing the Z axis / Knee screw be aware that with ball screws the weight is likely to 'self unscrew' it. To prevent this my Beaver CNC mill has a brake mounted directly on the screw which is 'normally engaged' and the controller releases the brake (24 volt actuated via a relay) when the servo system wants to rotate the screw. In this mode the servo prevents unscrewing. Without this if power was cut off the Z axis would crash down on it's own)

I had experience of this the other day - Z had over travelled it's limit switch due to a fault in the tool changer (it's a travelling column mill) and the only way I could move Z down within the limit switches was, with power off, climb into the enclosure, and apply 24 volts to the brake to release it and let Z fall onto wooden cribbing - it only had to drop an inch but being in the enclosure standing on the Y way covers was very alarming!

 

[minimutly]

When you come to replacing the Z axis / Knee screw be aware that with ball screws the weight is likely to 'self unscrew' it. To prevent this my Beaver CNC mill has a brake mounted directly on the screw which is 'normally engaged' and the controller releases the brake (24 volt actuated via a relay) when the servo system wants to rotate the screw. In this mode the servo prevents unscrewing. Without this if power was cut off the Z axis would crash down on it's own)

I had experience of this the other day - Z had over travelled it's limit switch due to a fault in the tool changer (it's a travelling column mill) and the only way I could move Z down within the limit switches was, with power off, climb into the enclosure, and apply 24 volts to the brake to release it and let Z fall onto wooden cribbing - it only had to drop an inch but being in the enclosure standing on the Y way covers was very alarming!

That's interesting - more to think about.
Thanks.

 

[fizzy]

Been working hard!
Be lovely to see it once it's been scraped.

 

[fizzy]

When you come to replacing the Z axis / Knee screw be aware that with ball screws the weight is likely to 'self unscrew' it. To prevent this my Beaver CNC mill has a brake mounted directly on the screw which is 'normally engaged' and the controller releases the brake (24 volt actuated via a relay) when the servo system wants to rotate the screw. In this mode the servo prevents unscrewing. Without this if power was cut off the Z axis would crash down on it's own)

I had experience of this the other day - Z had over travelled it's limit switch due to a fault in the tool changer (it's a travelling column mill) and the only way I could move Z down within the limit switches was, with power off, climb into the enclosure, and apply 24 volts to the brake to release it and let Z fall onto wooden cribbing - it only had to drop an inch but being in the enclosure standing on the Y way covers was very alarming!

Sounds seriously dodgy

 

[minimutly]

Sounds seriously dodgy

Progress today:-
The tapped holes in the knee are awful close to the edge of the new dovetail - either that or the are awful close to the surface of the scraped face - which I guess could be bad news.
Any views anyone?

 

[minimutly]

I've centre punched 2 rows, but I guess it's decision time?

 

[Fastdruid]

If it helps I believe the recommended minimum (in cast iron) is 1.5x bolt diameter from the edge to the centre of the taped hole.

 

[minimutly]

That's usefull, thanks

 

[fizzy]

I didn't mean your work was dodgy - I was referring to awemawson climbing into the enclosure!

 

[minimutly]

I didn't mean your work was dodgy - I was referring to awemawson climbing into the enclosure!

Lol, no worries. There are some things I'd like to do better though, but hopefully will get some advice from the expert next week. Right now I'm fighting the urge to drill and tap the knee to attach the new dovetail, mostly by feel, since I don't have a way to measure it...

 

[pressbrake1]

If it helps I believe the recommended minimum (in cast iron) is 1.5x bolt diameter from the edge to the centre of the taped hole.

That’s thread depth

 

[Fastdruid]

That’s thread depth

No, it's not.

I mean, yes it also is but I did specifically mean for the distance from the edge.

I googled it previously and found a vast array of figures (with a whole load of confusion from the civil engineering standards) but most seemed to be suggesting about 1.5x diameter (and about 2.5x for aluminium).

Has to be noted of course that this is for the *full* strength of the bolt to be used and that is rarely the case, particularly in things like this where its less carefully calculated and more massive overkill!

EDIT: I should also say I'm more than happy for you to tell me "no, you're wrong, it's Y times bolt diameter", I'm not precious to being told I'm wrong by someone with more experience/knowledge.

 

[Robcorrie]

Is there any chance of letting me know what horse power motor is on the turret. I’ve just done one of these up, it has a 1/4 hp single phase motor and struggles however I don’t want to replace it with anything too large and wreck the gear box
Thanks in advance

 

[minimutly]

Just checked, it's a 1 hp, 3 phase.
This is on the mk2, mk1 may have been smaller I believe?

 

[Robcorrie]

Thanks for that, mines a mk2 too, think it’s just had incorrect motor stuck on it at some point. I can fit a replacement 1hp motor now with confidence, I’m impressed with mine so far, many thanks

 

[minimutly]

Well mine's in bits still, scraping the vertical ways before moving on to the knee. Getting closer, and looking forward to using it, and especially the notcher.

 

[minimutly]

Some progress on the front ways, and the dovetail behind. Very little wear -around 1 thou, which is nothing until you apply some blue and a straight edge...

 

[minimutly]

Thanks for that, mines a mk2 too, think it’s just had incorrect motor stuck on it at some point. I can fit a replacement 1hp motor now with confidence, I’m impressed with mine so far, many thanks

Have you used the notcher yet? @Robcorrie

 

[minimutly]

Latest update on this, I had a Horizontal universal (Midgely &Sutcliffe Richmond) mill come up for sale near me, so I had to get a move on. I se the new dovetail using the remains of the original and a ground rod (gudgeon pin) and a tenths dti and 123 block - keeping both the ways parallel. It might be miles out of square with the vertical ways but it's a start. The new dovetail is screwed in with m8s for now - if it's right, or when it's right I'll use a taper pin each end and some m10s.
I'm on the Gower on my hols(well 2 days) so pics will have to wait. I'll start a post on the Richmond....

 

[fizzy]

Well you certainly have the weather for it - too hot for me - 30C in Swansea today.
That miller sounds interesting - you now have 3! I only have 2