Harrison saddle lock

[Fastdruid]

And finally here's someone else's photo of under the saddle of a slightly different one than that diagram. It has a combined wear strip + locking plate, with a V cut in the middle of the plate to let it flex.

https://flic.kr/p/8vYRFf

Ive been in the saddle a few times, its not too much grief to take it off if you take the right hand end of the leadscrews off, then slide the screws to the right (provided you have room!) then the apron comes out downwards when you release it irrc but its been a few years now. Doubleboost's videos above are worth watching because the 11" and L5a are pretty close. My Harrison is a bit ship of thesus now, it was originally a 3 speed leadscrew with threaded 2.25" nose chuck but now has a 11" norton box with modified leadscrews, a L00 spindle and all sorts of other mods. You have to keep improving things right...
I had a really old L5 originally and when I took the wear strips off, they had big wedges wore into them which allowed the saddle to lift, so it can be educational to look at these if you have the sensation that the saddle lifts under heavy load.

Yeah, that is my photo and mine *doesn't* have a V cut in it. It's a solid block...

It also did absolutely nothing. My theory is that it worked when brand new but was marginal even then. Mine is however a very very old 1940's L5.

To make it somewhat more effectual I took a chunk out with the mill (so it looks more like the exploded diagram of the later models), it's still not great (might need a slit in it to work better) but it does at least work.

 

[Agroshield]

My theory is that it worked when brand new but was marginal even then.

Axis locks in general do not seem to be very sophisticated: think how a lot of them just bear on the gib strip and push it into the sliding way.

The type you show might be improved by converting it to a version of a split cotter (like on a drill press table-to-column lock). Bore out the thread for the locking bolt, put a female-threaded cylinder in the hole (maybe made of bronze).

It would need something that prevents it from rotating but allows it to move up and down. This could be a slot up the side and a pin through from the main part or making the hole in the cylinder eccentric (See Myford design below). That way, the locking device is independent of the saddle-underguide device.

 

[Fastdruid]

Axis locks in general do not seem to be very sophisticated: think how a lot of them just bear on the gib strip and push it into the sliding way.

The type you show might be improved by converting it to a version of a split cotter (like on a drill press table-to-column lock). Bore out the thread for the locking bolt, put a female-threaded cylinder in the hole (maybe made of bronze).

It would need something that prevents it from rotating but allows it to move up and down. This could be a slot up the side and a pin through from the main part or making the hole in the cylinder eccentric (See Myford design below). That way, the locking device is independent of the saddle-underguide device.

View attachment 451208

I think the issue particularly with the Harrison design is that it actually performs two functions, both as a saddle lock *AND* to prevent the saddle lifting. Two independent functioning blocks would be far better.

 

[RonnieM]

The block in fastdruid’s photo is the same as mine, I did think of cutting it in half and will do if it doesn’t work. I recon it won’t turn if the side that holds it in place is bolted tight, just one would need to be careful not to loosen the clamps bolt right back or that part of the block would fall out.

 

[jmp49]

How about cutting most of the way through it but leave say 2.5-3mm, then the bolt can flex the half of the block with the lock bolt in it independently with only the 3mm left to resist?
This I think is what fastdruid is describing above already.
A sort of basic flex joint & this would also keep it in its original place mostly doing its original job too.

 

[Agroshield]

...I did think of cutting it in half

I think that would be a bad idea. In normal use it has to be a little slack for the slide to slide and it therefore has the chance of shifting and jamming things up.

As above, if you want to tune it up, make a flexure in it. Do not just cut straight into it. Drill (and ream) a hole at what will be the bottom of the slit and saw into that. That way you are not leaving square edges that are stress raisers. The better the finish on the surface that flexes, the longer its fatigue life will be.