Tom Senior LV modifications.

Here’s a previous thread which might have been useful : **LINK**

https://www.model-engineer.co.uk/forums/postings.asp?th=119748&p=5

... but unfortunately the relevant photos have been removed.

MichaelG.

Thanks Micael will read through the thread later.

Steve.

My memory could be at fault, but I thought the knee lock screw pressed against a captive brass piston which was in contact with the main body of the mill. The gib has a hole through it for the brass piston. If the gib is adjusted and then locked by the bolts, the lock screw would not work just by pressing on the gib.

Will have a look at that tomorrow. I did look down the hole but only saw shinny metal. I think the best way would to block up the knee & remove the gib for inspection & a good clean & lube.

Steve.

Use some blocks of wood to rest the knee on and possibly a prop to stop the weight of the bed leaning forward and straining the knee screw. Or centralise the bed and use larger blocks to support either side, watch out for the Xaxis screw.

Yes , that is what i did.

So i removed & gave the gib strip a good clean. It was not really dirty. As you stated it has the brass slug in there at the angle of the dovetail. It looked as new. I refitted everything & left the 3 front screws just over hand tight

Adjusting the 3 gib screws over a few times back & forth until the knee went up & down without too much effort. ( the bottom 2 to 3" did get a bit tight as you had mentioned, wear etc).

After everything was replaced & adjusted i turned on the DRO & did the same test as yesterday. Exactly the same. 0.01mm. So as Michael commented maybe it is the best it can achieve.

Steve.

Have you tried a similar test with the X and Y locks? It is common for the locking action to move something, even a thin film of oil can be squeezed thinner. You only need to take something like that into account if the tolerances expected are tight. It would be normal practice to lock the axes which are not going to be moved before cutting metal. I always lock the quill before taking a cut also.

The massive gib in the knee is, I'd suggest, preferable to the common thin strip type - certainly in this application - although it can be more awkward to adjust. The table/knee assembly effectively hangs on the female dovetails, if the support from the raising screw is removed, as in lowering the table. This puts the hex-head bolts into tension, so, for rigidity, they should be tight, not left loose enough for gib strip movement.

One problem with this type of gib is that tightening the retaining bolts can (will) cause the gib strip to move. When I adjust such a gib, I try to do it with the sliding member supported, but free to move (counterweight), or even with the machine on its back (grunting and gorillas required). The retaining bolts are slackened only enough to allow (somewhat difficult) movement of the gib strip, when pushed by the adjusting screws. If the adjustment makes the slide too tight, it's necessary to thump the knee to bring the strip back into contact with the slackened-off adjusters. When the adjustment seems optimal, tighten the retaining bolts, whilst thumping the knee to ensure the strip remains in contact with the adjusters. The slide will probably tighten as the retaining bolts are tightened, so go around the cycle again (and again)... And, of course, the gib adjustment has to be a compromise because of uneven wear (and/or original machining) along the slide's travel.

As has been said already, the locking pad is independent from the gib, so will produce a sideways force to the knee and it's not surprising that there will be a tiny movement as any oil film is squeezed.

Yes the X & Y are both ok . No error reading when nipped up. I will do as Kiwi Bloke suggests. As previously said it is very minimal but just a pain watching the readings as the lock is tightened up.

.

You’re right, Steve

When the display is showing 39 it tends to appear significant ...

but it’s worth keeping things in perspective :

Here’s a useful ‘benchmark’ image, courtesy of Wikipedia:

.... a 50 micron human hair, and a 6 micron carbon filament in the same frame:

**LINK**

https://en.wikipedia.org/wiki/Micrometre#/media/File:Cfaser_haarrp.jpg

May I suggest you print a copy, and hang it near your DRO for Zen contemplation ?

MichaelG.

.

The scale bar at lower-right is the distance you are concerned about

Edited By Michael Gilligan on 03/11/2020 09:02:08

Well put into perspective it is not that bad. Thanks Michael.

Steve.

I have started on the new nut for the knee Z axis. The length of leaded gunmetal, sae 660 has the bore opened up to 0.8" as the starting size for 1" X 5 ACME. I have to make a tool to hold the IR22 5 ACME insert. The tool is being made of an unidentified bar of something that looks like a high tensile stainless steel. The angle of dip for the insert is 14 degrees and I have left the helix angle at zero as the tool may be used for right handed threads as well as the left hand thread I will be cutting. The actual helix angle for 1" X 5 ACME is 3.65 degrees, I might have to give the insert a little added relief before cutting the thread. This is a time that a rotating base for the vise comes in handy. The bored gunmetal was parted off with a little added support from the tailstock and I used a 26mm 2mm wide Kennametal blade with an A2 insert. Gunmetal is one of the easiest alloys to part off. The threading tool will need some slight mods to fit the bore and I have to wait until the internal threading insert arrives from APT. Being a left hand thread,I can use a righthanded tool and thread away from the chuck which is much easier.

Edited By old mart on 04/11/2020 19:33:25

Edited By old mart on 04/11/2020 19:35:25

That will be interesting to see how the job develops old mart. I fear mine has the dreaded wear as on occassion the table drops. usually when it is low down. Tight gib sindrome.

Today the new drive motor arrived. It is for a Bridgeport X axis , which i am going to use for the Z axis. Everything is wrong dimension wise so new bushes & mounting plate to make. The Brass crown wheel needs boring to the Tome senior size. Lots to do & looking forward to doing it.

If all goes well it may add a few extra years to my weary shoulder.

Steve.

Edited By Steviegtr on 04/11/2020 22:48:05

I cannot see exactly how one of those drives can be shoehorned into position for the Z axis. There is very little clearance between the chip tray and the knee at the lowest position. Also, one of the reasons I didn't make the long handle for the knee a permanent fixture was because it got in the way of the operator. I would love one on the Xaxis for the museum's TS.

old mart you are spot on with your comment. I was hoping the drive was a bit shorter than it is. I tried to get dimensions before i bought it but could only scale it in my head from watching youtubers fitting them. Size of hands etc.

I am going to loose around 75mm of lower travel. On the plus side i will still have 330mm of useable room, bed to quill. I have not so far needed the bed to be that low down. Now i have said it Sods law will prevail.

In fact until i fully lowered the knee tonight, i did not realise how far it went.

I am still going ahead with the job. I guess in the unfortunate circumstance i ever need the extra room i could always remove temporarely. Made a sleeve bush tonight for the central needle roller bearing & will be going forward tomorrow with other bits. I am filming as i go.

Steve.

You do not have to fit the feed unit hanging vertically, it can be fitted rotated clockwise, to regain the lost travel.

It's quite common to see them fitted off vertical, to clear the Y axis feed unit fitted on some machines.

Nick.

Edit:- Worth noting, that the dedicated Z feed units come with a different feed direction lever, to that fitted on the X axis units.

Edited By Nick Hughes on 06/11/2020 10:55:59

Yes Nick ,the operating lever, luckily being where it is will miss the hand wheel once put back on. At right angles it may have been a knuckle basher. I tried holding it asqew & it looked a pigs ear. Also on its side it will cop for all the swarfe in the controls.

Steve.

If the unit would be ok at right angles in your case, you would not loose that vital Z travel. I am still worried about the low torque from most of these units, there is a slightly more expensive that has almost three times the torque. I think you will burn out the motor very quickly.

The reason I added that cranked lever was because of the high ammount of effort needed when the loading was high and the knee was low down.

Just seen your reply old mart. You may well be correct as the burn out. Something i will not know until it is done. The right angle approach is spot on. I have just finished machining the altered bridgeport end plate to fix to my knee casting. I held it in place & rotated the whole unit. I have it at 90 degrees & the only thing causing problems so far is the control lever being in the wrong place & hard access to the speed pot.

I removed the roll pin which gives the handle its travel limits & have re drilled the pin elsewhere so now the handle is square on with the machine. Just the speed pot to sort out. It is just catching the X axis worm gear. Stopped for tea so some late oil to burn tonight. I may need to make a guard for the unit though, as now it will catch all the swarfe.

Steve.

Some of these units on ebay have a claimed torque of 450 inch lbs, they would be ok, but the others may be 135 inch lbs which would be fine for the X, but not for a loaded down Z. Maybe you could fit it to the X and use the motor that you have already fitted, possibly with further reduction on the Z.

Nick Hughes has an Align unit which is more powerful on his Z axis.

Edited By old mart on 06/11/2020 18:36:54