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Locking up my cross slide
bogstandard:
I am really digging deep to come up with quickie projects, so this time, it is another on modifying my lathe, the technique used can be used in other projects as well.
Although I only purchased my lathe last year, it is an upgraded version of a fairly old well proven design. That was one of the reasons I chose it, any major problems were sorted out years ago. My problem is that mine is the first reincarnation with the DRO's fitted. I have recently found out an even newer version is available where they have swapped the front on the apron around, swapping over the half nuts selector handle and the saddle feed wheel over, to the civilised position, where you don't get your hand covered in blisters while feeding towards the chuck, burnt by flying red hot swarf. It seems though that they haven't put right the problem I am about to solve.
The problem being, when they fit the read head to the cross slide, it covers over the grub screw that is used to lock the cross slide. This is a real necessity if you are cutting heavily or doing final finishes. The head could be moved to the other side, but under certain conditions, you would lose over 1" of travel towards the chuck, and also the head could be liable to damage from the turning chuck.
So this post will be done in two parts. The first showing what I will be doing, the second actually doing the job. An afternoon should easily see this job done.
So here is my proposal.
The top bit shows how the normal lock works. Tighten up the grub screw, and it pushes the gib against the inner dovetails, that action effectively locks everything up.
That method cannot be used on the other side, as there is no gib strip to protect the precision face of the dovetail.
The solution is shown in the bottom sketch. An angle machined on the end of a bronze piston will be the bit that contacts the dovetail. The other shown bits will be explained as I do it.
It just fell apart in me 'ands boss.
It was honestly that quick, a few minutes and the bit I was after was free of the machine
While I have parts like this off a machine, I always take the opprtunity to look at the bits that will finally wear out. If it is a complicated bit, I would measure and draw it up, and most probably make a spare some time in the future. This time, it isn't needed. I know I could knock one of these out in a couple of hours from a lump of bronze, so no need to carry spares. It also has basic backlash adjustment on it, so it could be adjusted and used while I make a new one.
If I did a cross section of the casting, this is what it would look like.
Also from the end.
I did a rough transfer of the normal locking screw position onto the other side on the casting. This position should be in the right place if the manufacturers have done their maths.
Having blued up, I transferred the line from the bottom to the side face, I now had my first position line.
The blued arrow is showing the position on the top face of the ball oilers. I don't want to remove them because they might be damaged. I must position the job in the vice so that they are outside of the jaws, otherwise they will get crushed and destroyed.
The dovetail on the machine was measured for height.
After a bit of mental working out, calculating with the diameter of the thru hole, I came to the conclusion that 6mm from the bottom would be an ideal position to drill the hole.
That dimension was duly drawn onto the upright line from previous times. The crossing point was was given a pop mark
Why didn't I just mark it up at half way, at 5mm? There is plenty of meat above the hole, but not a lot below. So to retain maximum integrity, I gave it an extra 1mm of meat below the bottom of the hole.
Because I don't want anything protruding from the finished hole, I need to know how deep to tap it without removing lengthways support to the bronze piston. I had a choice of three different lengths, and have decided to go with the shorter one. The maximum operating range of the grub screw will be less than 1/2 turn, and hopefully massive forces won't be required to lock up the slide, so a 6mm long one should be perfectly OK in this situation.
Because the piston hole will be the same as the tapping size for the grub screw, if it feels a little fragile, I can easily tap a bit deeper and shorten the piston.
So that's it, any questions before I start drilling?
Bogs
Darren:
Quick Q
Are you planning to put just the one on the non gib side because your DRO is in the way on the gib side, wasn't too clear in your post. :scratch:
bogstandard:
That's correct Darren, because of the manufacturers mounting the read head on the locking side, I can't lock my slide up as it is. The locking grub screw is covered over by the read head.
After tomorrow, the problem should be solved.
John
Darren:
Gotcha :thumbup:
Stilldrillin:
--- Quote from: bogstandard on March 26, 2009, 06:30:02 PM --- So that's it, any questions before I start drilling?
Bogs
--- End quote ---
No questions.......
Just watching, quietly...... :thumbup:
When tightening the toolpost, I hand pushed the tool into the rotating chuck jaws the other day! :scratch:
Soo... I started making my mini lathe carriage lock yesterday! :wave:
David.
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