Thread: Brobo Super 12 cold saw freshen up

I'm currently doing a bit of a clean and freshen up on an old Brobo "Super 12" cold saw.

Here's a photo of what it was like when I picked it up.






It was functional, but had a substantial oil leak from the spindle - so at least needed new seals. To get the spindle out requires a complete strip of the worm drive in the gearbox, so its getting new bearings and maybe a lick of paint while I'm at it.

Interestingly, the spindle runs directly in the cast iron housing. The bearing surface area is pretty substantial and in decent condition for their age.






The only rolling element bearings are a decent tapered roller at the motor end of the worm shaft, and a smaller deep groove ball at the other end.








The keyways in the worm and motor shafts are badly worn. I'm tossing up whether to just try and improve them by welding and recutting, or alternatively fit some sort of coupling like a Lovejoy. I'm open to opinions or alternative repair methods so let me know what you think.

Steve

The keyways seem to be well ab used. Would you be able to machine the keyways bigger and fit a larger key to it. Had that done to a crankshaft, where the timing belt pulley fitted, on a vehicle once.
Kryn

Originally Posted by KBs PensNmore

machine the keyways bigger and fit a larger key to it
Kryn

A rectangular key would do the job, if you weld it it will bend a bit and the shaft is most likely 4140 so the weld could be a bit tough on an endmill as the weld will pull out some chrome and carbon.

You mean a larger rectangular key on the motor shaft?

Steve

Originally Posted by OxxAndBert

You mean a larger rectangular key on the motor shaft?

Steve

Yes..... i was looking at it wrong, the motor shaft won't be 4140 but i think you would run into trouble if you weld it as when the weld cools it will bend the shaft a bit and it might be a problem to realign. Cutting the corresponding internal keyway will be a fun exercise for you.

I reckon you're right about the welding John. The more I think about it the less I like the idea of messing with those keyways.

A L095 size lovejoy coupling is about the right diameter (53mm) to replace that collar thing on the worm shaft, and I assume that coupling style works OK since the later model saws used them instead of the keyway (albeit the next size up - L100 which is 64mm).
With the rubber spider in the coupling to absorb any shock loads, I reckon if I make a press fit drive flange to go on the worm shaft, and a keyed one to go on the motor it should work OK. I might have to plug the original bore in the worm shaft so it doesn't shrink when the flange is pressed on.

I've ordered a rubber spider from ebay, so will make up the flanges to suit when it arrives.

Steve

Back onto this project after it got bumped by higher priority ones.

The main pivot for the head was worn - both the shaft and the bronze bushes in the bore.
The bushes had plenty of thickness so I decided to bore them out a bit to true them up, then make an oversized shaft to suit.

Got the saw casting roughly clamped and could see first challenge was I didn’t have a long enough boring bar that would fit in my boring head.



Toyed with modifying a bigger one or brazing some carbide onto a bar to make one, but then remembered I had a lump of HQ Holden anti-roll bar (spring steel) that I’ve had since 1988 (yes, that’s sad on many levels) and I knew it hardened up well.



It was beautiful to turn with a cheap Chinese round insert.




Gave it a rough grind, heated it red hot and quenched in water then a quick sharpen.



Worked nicely, but I wasn’t happy with the work holding and alignment.

Made up a spigot that was a close fit in the main spindle bore of the saw casting, and bolted it to the table then lowered the casting onto it and clamped it down. This way pivot axis would be nicely aligned with the saw spindle.






Bored the bushes out until they cleaned up then used the facing feature of the boring head to face the casting.



Now, how to face the other end of that casting - the one that bears against the saw base casting….??

Ended up with this setup.
Casting clamped to box square, set the bore up vertical with a square then supported it with a machinist jack and clamped down.
The indicator was so I could see if the casting was moving during the cut (it didn’t)





Took a few light cuts with my favorite face mill and all done.



Ended up with about 0.1mm variation measuring across the faces. Plenty good enough.
Since I knew the first face was perfectly aligned with the bore (done in the same setup) if needed I could have scraped that second face to get it better.

Next challenge is making a 36.90 diameter shaft from 38mm stock….

Steve

Got the shaft finished tonight.
Cut a small flat on it for the grub screw in the lower casting to bear on, should make it easier to pull apart in the future if I ever need to as there won’t be a burr on the shaft to bind in the bore.



Faced off the mating surface of the lower casting.



I could do with some suggestions for the next challenge though.

Threaded shaft on the base of the vice that goes through the main fixed base and has a cast iron nut underneath to clamp it.
Vice is upside down in the photo and you can see where I’ve cut off the bar that tightens the nut (and evidence that you can sort-of stick steel to cast iron with a MIG..)
That clamping lever/bar extends through the opening in the side of the base - so you have about 150mm of swing to clamp it.




Problem is that as things wear you run out of travel in the slot to clamp it.
Apart from the bar being “welded” on, there were also shims in various states of damage when I pulled it apart. Clearly thin shims don’t survive in that shear/clamping application.

I’d like to have an easy way of allowing for the wear, and to get it adjusted to clamp properly for starters.
The best idea I’ve come up with so far is to spline the nut, and make a splined collar to go over it that the clamp handle attached to. As long as the spline is fine enough so the angle change between splines is less that the angle of the handle opening I think it should work. Collar could be retained a number of different ways, but a circlip underneath it would be easy.

Anyone got a better/simpler suggestion to allowing for adjustment?

Steve

A splined setup scores high for elegance, if you can create a splined system without too much difficulty.
Splineless me would consider attaching a disc to the nut (or boring a new nut thread in the centre of a suitable disc), and fitting the lock lever into radial holes around the disc, or bolting it on using holes parallel to the screw axis. Either way needs holes spaced to allow adjustment as fine as you need. Lacks elegance, but may be more doable.

Hi Steve,

You could always turn a couple of thin Nylon washers to sit on either side of your shims, that will help to protect them from damage when tightening the vise. Or simply use a Nylon washer of the right thickness.

Ehat if you were to back it off one full turn and use a thick shim, grind it as necessary.

Thanks guys.

The initial adjustment isn't too much of a drama. As suggested I could use something thicker than the thin shims that were there.
Main issue at that point is attaching the clamp handle, and then taking up any wear later on.
The wear may be a non-issue anyway seeing as its not in a production environment so won't see much (ab)use, but it would P me off to find that it settled in and I ran out of range for the clamping handle after deciding on a fixed handle approach.

While my spline idea would be really nice, as WCD said there ways which are more do-able.
The external splines are easy. The internal ones not so much, although with having the shaper I have the capability.
I'd also never need the full 360deg of spline range as the clamping screw pitch is quite coarse, and it will never wear that much.
So, started thinking about a simple partial spline, and realised that's realistically a keyway!
But a single keyway doesn't give any angular adjustment, so it would need at least 2 keyways in one of the pieces.
2 keyways means they can't be very close together, and may still not give a small enough angle.....
Next thought was that your usual ROE spanner has the end offset at an angle to the length so that turning it over gives a different rotational position of the jaw/ring. From memory it might be 15deg which would be half the 30deg of each point on 12 point ring...
So I'm now thinking:
Cut 2 keyways in the existing nut
An outer collar to go around that also with 2 keyways - but in slightly different in angular position to the nut
The handle fixed to the outer collar between the 2 keyways, but not exactly in the center.
If my brain is working properly and design is right that will give 4 positions:
key in left slot
key in right slot
collar inverted and key in left slot
collar inverted and key in right slot

Sounds complex but I think the hard bit is in the design of where to put the keyways and handle, not in the construction.
I'll draw it up later as the description above might not make any sense outside my head

Steve

Hi Steve, Guys,

In that case why not just cut off the protruding bit on the nut, give it a spin in the lathe and then mill six flats around it to suit a ring spanner. If you want to retain the spanner, so it doesn't fall off the nut, an "O" ring would do that !

Good idea John.
For a start I thought it was still going to be too coarse. I measured tonight and I've got about 27deg swing in the clamping slot, so with a 12 point spanner (30deg between facets) I wouldn't quite get enough movement to get to the next notch on the spanner.
But, continuing on with the slight offset of the handle idea - a 5deg offset of the spanner head from the handle centreline would give a 10deg movement when turned over.

So, start off with the table locked tight, and the handle approx 2/3 across the opening (18deg from the start of opening).
Things wear a bit, and the handle progressively moves in the range until it touches the casting.
Flip the handle over, and it moves 10deg back towards unlocked position, so we have space again to clamp.
It wears another 10deg until it touches the casting, so you turn it back over to the original way up (lose 10deg) and then move it back a facet on the spanner (gain 30deg) so overall movement is 20 deg. Puts you about 2/3 back in the slot and you have another 20deg wear before you run out of swing (and can start the whole sequence again).

Minor things to cover off such as:
1. the hex on the nut has to be horizontally in line with the slot - since the handle can't have any vertical offset if it needs to be turned over
2. depending on where the existing nut sits and how long the shaft thread is will determine how I actually do it - ie whether I can just cut the hex onto the nut or have to make a new longer nut or extend/space it down somehow to get in line with the slot.

Good idea with the O-ring retention too!

Steve

Happened to have an old 1-13/16 knocking spanner (think that's what they are called) that doesn't get used.

Knocked off the old weld and handle stub from the nut, and turned up a quick mandrel to mount it on since there wasn't a decent reference surface on the outside. Made it easy to work out the final dimension across the flats.
Proceeded to mill a hex on it. The remaining spots of weld were pretty hard so I just hand fed those to make it a bit easier on the cutter.




There was a moment of excitement though, as what I *thought was just another weld area turned out to be the stub of the original handle that had been threaded into the nut.
The cutter spun it out and chewed it up by the time I hit the feed stop button, and it rotated the nut slightly. The old stub is the mangled lump sitting next to the hole it got ripped out from..
The finished hex worked out well, as it left all the original clamping surface on the end of the nut.





Spanner fitted nicely, but I ended up turning off a section of hex so I could sit the spanner at the top of the nut, run the nut up until it touched the saw base and then drop the spanner down onto the flats.





The theory of the 12 point facets and the slight offset of the spanner head worked really well. When I couldn't get enough movement to tighten it properly, I just removed the spanner and flipped it over. Perfect.




I haven't decided on a handle extension yet, but its functional as-is so good chance it will still be that way in a few years time.

Edit: with the nice fit on the nut and the spanner sitting in the slot, it can't actually come off the bottom of the nut - so no need for a retainer of any sort.

Steve