Thread: Cross slide scraping

Originally Posted by Michael G

Thinking about the problem some more, you'd need something like a 14" long sine bar with a deep top beam to minimise deflection.
Clamping would need to be done across the parallel sides, so would need to be at the dove tail angle to the table. I can see a day+ to make up a jig that would be used once. Paula's concept of a set of forum loan tools & jigs makes a lot of sense...

Michael

I read up on the loan tools, & they do make very good sense. A good idea.
Also over time have appreciated what Paula has accomplished.
A very capable person.
regards
Bruce

Hi Michael,
My current thinking is that the vices will be able to grip the taper.(though that will be about 1.25mm across the width of the jaws)*

If I was brave enough I could cut the old gib in half and use that as packing.

We'll see.

Stuart

*Well that didnt work. They didnt even get close to twisiting far enough. On my "good" vice I could lossen the gib but I only have the one. oh well on to plan B

Cut the gib off this morning. Didnt leave a big enough flat, but thats easy fixed.

Then on to plan B which was to pack the soft jaw. Clamped the gib loosely in one vice and tightish in the other. slipped a piece of 1mm packing in behind the soft jaw until it wouldnt go any further, loosen that vice, push the packer in a little more and tighten, repeat on the tight vice.

Plan B only just worked, if the gib had been much higher or thicker the saw wouldnt have been able to reach.

Its way over size as although I carefully measured and set up the mill I wasnt game to trust myself and worked to a scribe line that I KNEW would leave me over size.

Tricky little things, I think theory would say you have to machine the angles from the sliding face. I have no idea how much difference it makes in the real world though.


Stuart

Originally Posted by Stustoys

Hope its right. My cunning plan was to set the cast iron in the vices with the old Gib on the top. Tap the cast until the top of the gib was flat to the X axis. Which means the cast iron is now set to the taper of the gib right?

Stuart

If that was me, I'd put the old gib under the new one. For that to work, it has to be slightly narrower than the new one. Or you use a couple of dowel pins between the sliding jaw and the new piece.

Then you tap the old gib in like a wedge or drift. The trick with a 14" gib, and an 6 inch vice. Your going to have 4" sticking out either side. Use that to your advantage. Put equal parallel strips either side of the vice. They can be above deck height of the vice, size them so you get maximum holding but can still make your cut.

I think I saw you mention 2 vices, even better, put a block in the middle, plus the 2 ends. Cutting forces will mostly want the two -over hangy bits spring down away from the cut.

The Brides away from tomorrow, I should be in on Sunday, if you want to go the double sided sticky tape, sine bar and grinder routine.

Phil.

Originally Posted by Machtool

"Cutting forces will mostly want the two -over hangy bits spring down away from the cut".

Phil.

That's the difference between us amateurs and a professional - he knows the right technical terms for these things!

I've attached a drawing of the point that I was trying to make earlier
gib (Large).jpg
The top represents the underside of across slide with an exaggerated taper on the slide and gib. Getting a good fit relies on the two angles being the same so that the face that mates with the carriage dovetail is parallel. The tapers are very slight. From memory, mine is around 1:50 may be less (1:70?). The bottom picture tries to show this with some perspective. The solid line is what a parallel gib would be. With the taper, it follows the dotted line. Point is, there is not a lot to hang onto and the faces that are there don't give much parallel either. I'm not sure I could hang onto that successfully. The thin end of my gib is only a bit over 5mm thick. That will be hanging out of the vice 5" (4" vice). Is there a less risk filled way?

Michael

I find the prospect of making a tapered gibb strip fascinating, mainly the work holding aspect which seems to present the biggest challenge.

Is it not feasible to mill the two main surfaces of the gibb strip on the mill with a face or fly cutter first. This would obviously produce a parallel gibb to start with. Then, using a flat piece of plate, say 1/2" or so (it may need to be faced both sides first) and at least as long as the gibb strip and hold the gibb strip onto this. Then, create the taper angle by sitting the plate on the mill and elevated at one end with the required amount to produce the taper (using such thing as a feeler gauge or the like). Then face the suface again to produce the taper. Then all it's matter of doing is to produce the trapezoid at the top and bottom, could this be done by clamping the gibb strip to the upper slide and milling down to the correct size?

By clamping onto a flat plate, it allows you to clamp hard at each end and not worry about movement up or down, as long as the plate is strong enough.

My simple brain is just trying to make this as simple as possible. Problem is, it's probably too simple!

Any thoughts?

Simon

Originally Posted by Michael G

That's the difference between us amateurs and a professional - he knows the right technical terms for these things!

I would'nt believe a word that guy says. He just had a major brain fart. Stu's gib is the twisty - twisty one. The sides arnt square. I was thinking box way not dovetail.

Phil.

Wow were to start

Originally Posted by Machtool

If that was me, I'd put the old gib under the new one.

I tried that but I dont have parallels to suit and would have to make them+ while the vices are the same I have never checked how close to "matched" they are.

They are long enough that there is little over hang at the ends even with a 460mm gib.

I may well take you up on your offer. I'll see how the scraping goes, also the flat ways of the cross-slide seems to bind(bind maybe over stating it a little, feel a bump now and then when sliding them over each other), after a second opinion as I might just be getting a little excited.


Hi Micheal,
All my machining was done holding onto the waste side. Due to the size of my gib I could have held the gib for the last cut but the set up would have taken much longer.

The way I machined the gib, the angle of the taper you are worried about(I think) looked after itself(I believe). What this picture doesnt show very well is that the width of the 35degree milled face tapers. (the top face will be the one against the taper in the cross-slide)

https://www.woodworkforums.com/attach...ing-cszzzp.jpg


Starting to think I didnt take enough pictures.


Hi Simon,

How are you going to hold the gib to the plate to machine the taper?



Sorry if I missed anyone.

Onwards!

Did some quick cycles on the 2 sliding faces. 6 on the face against the dovetail. 9ish on the face that rests on the flat way.
Its looking pretty good so far(to me, but what would I know?),. One problem might be that most of my extra height seems to have gone, which is a worry because I thought I was way over and there is no way I took that much off in 9 cycles.
The slide is 337 long, the gib is 460 long and I currently have 135mm over hang left. with luck I wont run out.

Stuart

Simon, that's the issue I'm mentally wrestling with at the moment - how to hold the gib onto the plate. Up until there what you have described is probably the way that it would need to be done (although I think I'd make the plate much deeper than 1/2" - perhaps weld a piece of plate onto some RHS to increase it's depth of section = less deflection).
My gib section at the big end is approximately 16mm x 10mm, so there is not much to hang on to.

Stuart seems to have produced what he was aiming for but the method he used relies on having a large chunk of material underneath the new gib to hang on to. My gib in waiting is a length of CI, 25x25. While the first two sides are easy and the third is slightly trickier it's that 4th side that is causing the mental processes extra time at the moment.

Michael

Hi Michael & Stuart,

WRT holding the gibb on the plate, I thought that maybe drilling and tapping appropriately sized and spaced holes to clamp the gibb onto it. The gibb is longer than necessary? clamp at each end?

Also, the thicker the plate the better, heavy angle iron or a small I beam even better, something with a large moment of area to reduce flexing.

Edit: Also, if the surfaced are nice and clean (as presumably they would be) then perhaps the middle section of the gibb could be superglued to the plate. The clamps would do most of the holding and the superglue would stop any intermediate flexing or lifting?
Cheers,

Simon

Hi Michael,
I dont recall, do you have a hoz spindle? or just a vertical? does you mill have a brigeport like head that can "nod"?

Stuart

H and V. No nodding, just side to side

Michael

Hi Michael,
I see your problem now. I haven't come up with any ideas that look like working out.

Meet up with Phil today who pointed me in the right direction.
First job was to make the inside top of the cross-slide dovetail parallel to the flat way. Now I could have fitted it in the mill getting into the dovetail with a boring bar I decided it would be easier to set up in the shaper.
Wasn't happy with the depth readings I was getting so used a couple of dial gauge bases to make a comparator.
Happy that the top is well within 0.001" of parallel to the flat way.
fingers crossed the gib will still fit.

Stuart