Tom Senior LV modifications.

[SteviegtrParticipant @steviegtr]

I forgot to post a picture of the finished item. In the end i had to tilt the motor as i had not realised when the X axis was driven to the far right, the end housing was going to hit the speed control pot.

Steve.

[old martParticipant @oldmart]

The thoughts of using the unworn end of my spare Smart & Brown lathe leadscrew will probably be shelved. It is 6tpi as against the 5tpi of the TS knee. Mechanically, this would be the easiest option, but the scale would end up being a compromise. the Z would be 83.33 thousandths on an inch per turn. I know some lathe cross slides have the 6tpi pitch with the result of a scale of 0-80, but I think I will keep with the 5tpi and 0-100 as the gearing is 2:1. I will check carefully any uneven wear and address that.

[SteviegtrParticipant @steviegtr]

Just a thought old mart on the length of the screw. If you remove one of the covers at the side of the nut base. Could you somehow see inside the cabinet for thread stick out. Or is that part enclosed around the nut.

Steve.

[old martParticipant @oldmart]

I don't think those covers would work, they are for coolant. The Z leadscrew goes down into a sealed tube to keep the coolant away from it. I could wind the knee as high as it will go and block it up. Then if the bolts holding the nut were removed, the nut could be screwed up the leadscrew and measured, and the depth of the tube could be measured as well. I want to find out the depth of the tube as I have enough bronze to make two nuts, and the magic word "antibacklash" comes to mind, but the length of the nuts and the length of the leadscrew are factors as well as the depth of the tube. If there is some leadscrew showing above the nut when the knee is fully lowered, then the antibacklash nut could be above the existing nut position. It is frustrating not to be able to even see the mill during lockdown.

[SteviegtrParticipant @steviegtr]

Posted by old mart on 12/11/2020 18:37:49:

I don't think those covers would work, they are for coolant. The Z leadscrew goes down into a sealed tube to keep the coolant away from it. I could wind the knee as high as it will go and block it up. Then if the bolts holding the nut were removed, the nut could be screwed up the leadscrew and measured, and the depth of the tube could be measured as well. I want to find out the depth of the tube as I have enough bronze to make two nuts, and the magic word "antibacklash" comes to mind, but the length of the nuts and the length of the leadscrew are factors as well as the depth of the tube. If there is some leadscrew showing above the nut when the knee is fully lowered, then the antibacklash nut could be above the existing nut position. It is frustrating not to be able to even see the mill during lockdown.

So you want to know the distance the screw has left when the knee is wound fully down. I could measure mine by putting a straight edge across the knee base & using a mirror/ camera see how much thread is left. Minus the distance the nut & holder stand above the cabinet , that would give you the gap you required to know.

Steve.

[SteviegtrParticipant @steviegtr]

I took a pic & did some measuring. This is the result.

Steve.

[SteviegtrParticipant @steviegtr]

If you want tomorrow i could chock the knee from the bed & undo & retract the Nut to see the length of the assembly.

Steve.

[old martParticipant @oldmart]

Thanks, I will be able to incorporate the antibacklash above the level of the existing nut easily in that length of screw. I will also add some sort of cover to keep the threads clean. The two nuts could be screwed into an external tube and the adjustment would be easy to do. That thread in your photo must me unworn as it never reaches the nut.

[SteviegtrParticipant @steviegtr]

I don't know much of my machines past life & not had it long. But with the knee fully down you only have 5mm of gap left. Is that enough to build in anti backlash.

Steve.

[old martParticipant @oldmart]

I may have misunderstood your first two posts of the 12th, I thought there was about 75mm of thread showing when the knee was fully down. Or are you saying that the base of the knee is close to the drip tray when it is fully down? If it is the latter, then nothing to worry, the knee backlash adjustment can be done with the knee partly raised.

[Simon Williams 3Participant @simonwilliams3]

Excuse me for butting in chaps, but…..

So long as the gib lock isn't engaged, If the weight of the knee isn't sufficient to overcome the friction of the gibs, in the Z axis, then the gibs are adjusted wrongly.

Given the weight of the knee is always in contact with the upper face of the Z axis leadscrew, there is no backlash.

There is still a modicum of backlash in the bevel gears conrolling the leadscrew; one would hope this was insignificant.

Rgds Simon

[old martParticipant @oldmart]

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.

[SteviegtrParticipant @steviegtr]

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.

[old martParticipant @oldmart]

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.

[old martParticipant @oldmart]

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.

[old martParticipant @oldmart]

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

[SteviegtrParticipant @steviegtr]

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.

[old martParticipant @oldmart]

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

[SteviegtrParticipant @steviegtr]

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.

[SteviegtrParticipant @steviegtr]

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.

[old martParticipant @oldmart]

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.

[SteviegtrParticipant @steviegtr]

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

Steve.

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