Tom Senior LV modifications.

Dead right, Simon, the problem is wear. The gibs are adjusted in the general most used part of the movement, and everything is ok until the knee is lowered right down for a tall job. I will address this when the knee is removed, but will only partially remedy the problem. I don't have the equipment or expertese to restore the ways to new condition. As the knee gib gets tighter near the bottom of its travel, the leadscrew starts to pull the whole weight downwards and as the nut has a lot of backlash, every so often the lot drops about 0.020", or whatever the backlash is. Having a quill, means that the knee movement is not essential for moving the Z axis while milling.

Hi old mart i am a little confused. I understand the wear & bump problem of which mine does a little bit. But you mention that by fitting a anti backlash screw above the original one will loose you some overall height. But you was saying you would like to put a 1" packing under the column to give extra height. It also bewilders me a little why you would ever need more than 16" overall gap with the knee down. My friend has a huge old milling machine & is so jealous of mine having more useable distance than his. Or am i missing something. If so apologies in advance from an old fart.

My defence is i live in West Yorkshire.

Steve.

I thought that living next to Lancashire would increase your intelligence. Your earlier posts seemed to show about 75mm of thread above the nut when the knee was down. Then you say there is only 5mm, which I hope is the clearance between the bottom of the knee casting and the drip tray. The thoughts of a 1" raiser for the column is some way in the future. If I were to put the 6" rotary table with a 5" chuck on it on the bed, there is an immediate loss of about 10" of Z height, that is without the workpiece or tooling accounted for. One of the reasons that the drill mill is being kept is the 3" extra Z available.

Too late to add to the last post. I have found some pictures of the boss which the Z nut is screwed to. I had forgotten that it sticks up from the tray. If necessary, I can make use of that height for part of the backlash mechanism.

Too late again, I have found a photo of the mill I had forgotten about.

Sorry to confuse with my architectural drawing. The top part of the picture is the knee with 75mm clearance from the underside of the knee casting to the thread end. At the bottom of the picture the nut & housing stick proud of the base by 70mm. Giving roughly 5mm clearance with the knee at it's lowest point.

Steve.

Thanks, I had understood your drawing when I saw a photo of the boss standing proud of the drip tray. I would make another one shorter. I would appreciate it if you could block up the knee again and unbolt the boss and screw it up the leadscrew to measure the diameter of the hole the leadscrew sits in. If it turns out a close fit for the screw, then I will have to think again about the whole antibacklash and just use one new nut, which will be much better on its own than the worn out one in use now.

 I haven't found any way to rotate photos when posting, but that one was to highlight the loss of height when tall equipment is in use.

Edited By old mart on 15/11/2020 16:11:50

old mart. I will give it a go tomorrow. I have some large blocks of wood to use as chocks. Will not forget to rope it to the dovetail so no pressure on the threads. I will take some close up pictures & post.

Steve.

Did it tonight for you old mart. One thing i discovered is that after you mentioned the bump when lowering the Knee i assumed mine must be worn too.

So when taking these measurements i put a lever under the Knee to see how much play there was in the Nut. The play in the nut is literally immeasurable. The bumping noise is from the top of the screw where it is connected to the bevel gear. It looks like the bevel gear is held in place by something like a cross pin of sorts, which can be rattled up & down. I assume it was made like this, as it always has a great weight on it.

Have you actually checked your Nut for play. It is a huge affair. Pictures & drawing below.

Steve.

Thanks, the hole looks like 1 5/8" diameter, so there will be plenty of room for part of a nut down there. It looks like you will end up removing the bed and cross slide to get at the knee mechanism. I can say that the tapered gib for the bed is removed from the left hand side and the X axis wheel and both endplates for the X leadscrew have to come off, then the bed can be slid off easily. After that, the X leadscrew will have to be unscrewed to get at the Y axis nut holding screw in the middle of the cross slide. After that, I can't remember. The whole lot is pretty easy to dismantle, we took the mill to bits and put all the bits on pallets when the museum inherited it.

To be honest old mart i am quite happy with it as is. It only bumps occasionally at the lower end.

Steve.