Tom Senior LV modifications.

The Tom Senior light vertical at the museum runs an R8 spindle upgrade and a 1hp motor rather than the original 1/2hp one. I fitted the 10mm link type drive belt to the machine, but it has proved not entirely satisfactory. Running up to 80mm shell mills has put more strain on the belt than expected. The trouble is that the belt has gradually sunk deeper into the vees of the pulleys and the metal washers on the link pins have started to rub against the soft aluminium, leaving a slight groove. I don't want this to happen, so the standard type of vee belt has been fitted. The size that fits this four speed machine is Z 18.5 10X 495Lp- 470 Li.

it's hard to find the hp range for Z section, but A section is good at low speed for 2.2hp on a 3" pulley or 1hp on a 2" pulley. More speed or more diameter = more power transmitted.

You might be running it outside it's design parameters with those shell mills. I guess the life you get out of the new belt will tell you.

As anyone who has seen some of my comments on link belting will know, i think they are for temp or impossible exceptions only. Far better to have a proper belt. How about changing the pulleys & using a toothed belt.

Steve.

One thing I found, that with the LV, you do not have to remove the motor to change belts. Just slacken off the pivot and locking fixings about 1/4" enables the motor to be lifted up by a couple of screwdrivers as wedges and the belt can be slid under the end of the pulley. The drawbar should be removed and the quill extended to get the belt past the front pulley.

Not wanting to start yet another TS thread, I have an improved leverage handle for the knee. This helps when there is extra weight on the bed, especially when the knee is near the bottom of its travel as there is less wear and the gibs are tighter. The handle I bought has seven indexing positions and I just made the mating adaptor on the rotary table at the 51 degrees and 26 minutes, which is not exact, but fitted perfectly first time. I was lucky guessing the crank on the handle, as there seem to be lots of variations for sale from numerous old mills. It just clears the tray at the lowest position without anymore than the minimum shaft extension. Most of the time, the original wheel will be fitted, but I like having the choice.

Edited By old mart on 29/10/2020 18:15:27

That's a nice addition. Sometimes when i am moving the knee from low down to much higher up, I always shout to myself dive,, dive,

Something i have been pondering over recently . A Z axis powerfeed with the ability to still do fine turns on the wheel. Without looking unsightly. Maybe something with a right angle gearbox with a through shaft to still house the wheel.

Going into Tier 3 on Monday here in Leeds , so maybe more time in the workshop,, again.

Steve.

An 80 mill shell mill on a light vertical,thats being rather cruel to your mill,it may have an r8 spindle and and 1hp motor but that does not make the machine capable of such hard work.

I don't push an eighty shell mill very hard, its the diameter that interests me rather than large chips flying about. Still even with 1/2mm of cut in cast iron or steel, the feed rate has to be fairly low. I listen to the sound of the motor, the six pole one has very good torque, as it runs below 1000 rpm at 50 Hz. The lower bearing for the spindle is one size up from the standard taper roller for an R8 spindle, the upper is the original size that TS fitted. The pulleys at the front run on needle roller bearings rather than the more common for TS bronze bearings. One of the reasons for going to R8 was the large quantity of R8 tooling we have at the museum. The conversion was very straightforward, but we had the great advantage of having a lathe and mill available to use in the workshop.

I have just got hold of a piece of gunmetal, 45mm diameter with a 17mm bore and 135mm long. It will be cut in half and make a new nut for the knee which is 1" X 5tpi LH ACME. Having a hole is great as I only have to bore it to 0.8" for the thread, which will be singlepointed on the lathe.

Edited By old mart on 29/10/2020 20:07:15

Edited By old mart on 29/10/2020 20:15:28

The 63mm which i tested out on mine cut nicely on mild steel & that's with the 1/2 hp & MT2. Like old mart says light cuts no problem. They are an extremely well made machine.

Steve.

Question from the experts. I have tried numerous times to adjust the gib on the Knee of my light. Posting a few pictures to show.

The top picture is the whole thing with 3 large bolts holding the quite large steel gib strip in place. There are 3 adjuster screws & a locking lever in the other plane.

How i did it was to undo lightly the large bolts & adjust the gib with the 3 adjusters & lock up. Then retighten the 3 large bolts. No matter how i do it there is always some error.

Example. I raise the knee using the handwheel & then zero the DRO. Then i nip the gib lock & the DRO moves by roughly 0.00039. I assume that is 0.39 of a thou.

It is always the same.

I guess i am adjusting the gib strip wrong, Anyone any idea of the correct sequence as i have no manual for this machine. OLD MART, Help. or anyone who knows the machine.

Steve.

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Steve,

With the greatest respect to Tom Senior [purveyors of fine machines to the gentry] ... I doubt if they were measuring to hundredths of a thou when they built them.

Methinks your DRO is too sensitive for comfort.

MichaelG.

Well i would agrre to your comment but the X & Y work perfectly. Just the z that moves every time i nip the locking screw. Maybe you are not the person i need to comment. Unless you have some experience of this fine machine.

Steve.

Your point is well made Steve

I shall simply observe, with detached interest.

MichaelG.

Edited By Michael Gilligan on 31/10/2020 06:43:23

No Michael don't do that. I was merely interested to know if you have had previous with the Tom senior then you would know whether it is correctable or not. If i am wasting my time trying to get it perfect then fair comment. I thought maybe there was a method i did not know about, due to the gib not only being adjustable from the side, but also locked solid by the front bolts.

Steve.

My point was very simple, Steve

0.00039” [which, for the benefit of Metricated readers, is almost exactly ten microns] is smaller than the tolerance to which I suspect the Tom Senior machines were made ... and it is very small in ‘general engineering’ terms.

I routinely work in microns on the microscope ... but not on the milling machine.

My assumption is that the action of locking your Z-axis pushes a pointed, or rounded, screw into a countersink in the gib strip, which then centralises and thereby moves the table slightly. ... The X and Y axes will behave a little differently, because gravity loads them differently.

I look forward to being corrected by those familiar with the machines.

... as I was taught long ago; it’s better to ‘lose an argument’ or ‘be proved wrong’ ... because after that, one’s knowledge has improved.

MichaelG.

I was just as baffled by the strange gib adjustment on the TS knee. Our one is easy to move in the top 2/3 of the range and then gets tighter in the bottom 1/3. This is the standard wear pattern presumably, and I might try and do something about it when the new knee nut is made. Because the large ammount of backlash in the nut caused by wear would not normally be noticable because of gravity, I chose to ignor it when the mill was put into working order. The tightness of the gib at the lower part of the travel causes sticking and then the whole assembly drops suddenly which I don't like. I don't know yet how much uneven wear there is in the leadscrew until it is removed. I would be over the moon if I could get the knee to 0.00039" on the museum's machine.

I am tempted to cut up the spare Smart & Brown model A leadscrew which I have, to make a replacement for the TS knee, it is 1" X 6 tpi ACME, which would require a new scale for the mill. I know it will never be needed for the lathe, but it seems just too vandalistic to contemplate until the TS knee screw is examined. I can even out the wear by singlepointing on the lathe and then make the new gunmetal nut adjustable for backlash.

Edited By old mart on 31/10/2020 19:06:19

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Having re-read that, Steve ... and looked at the photo : I think we need to see some detail of the locking mechanism

MichaelG.

As I recall, the bolts have some clearance in the casting and are threaded into the gib. They need to be slightly loose, say a couple of foot pounds only so that the adjuster locking screws can push the gib into the dovetail, then the bolts are tightened. It is one of those frustrating adjustments which would get easier with practice, but with only one knee to adjust, you are not likely to actually get much practice.

That 0.00039 figure with the DRO sounds like some conversion between imperial and metric, 1mm is close to 39 thousandths of an inch.

Michael & old mart. Thank you for the replies. I have put some pics below to show the error in metric & imperial. Also the adjuster removed. This adjuster acts against the back of the gib strip as the most others are, there is no brass slug in there.. The strip as seen is a pretty huge chunk of metal. Old mart may have hit the nail. It sounds logical to not have the 3 front bolts set too tight. Which i may have done. Will have to give it another go.

Steve.

Just to add. I have ordered a X axis powerdrive motor as retro fitted to the bridgeport. It is for the Z axis. This is much cheaper as it does not come with the shaft extension kit of which i do not need. I will need to make an adapter plate to make it fit.

I am going to take photo's of the mod & video. So if it is a success will post once done. It will still retain the handwheel for fine adjustments. Fingers crossed & hopefully not burnt.

Steve.