Precise filing

[Adam McCulloughParticipant @adammccullough31948]

I need to widen a narrow but irregular clamping slit in a casting so that I can insert a packing piece to clamp down onto. Access dictates that I need to do this by hand.
Can anyone suggest a suitable approach to filing or otherwise opening out the slit to an accurate and uniform width?
I imagine there may be some sort of file shape suitable for this job?
Thanks in advance

[Adam McCulloughParticipant @adammccullough31948]

[Henry ArtistParticipant @henryartist43508]

Without a little more information it is difficult to give a meaningful answer…

What are the dimensions involved?

What is the material?

Can we see a picture?

[Michael GilliganParticipant @michaelgilligan61133]

Adam,

You may want something like the Valllorbe LP1168 **LINK**

http://www.vallorbe.com/umv/ch/fr-ch/file.cfm?contentid=5308

… But Henry's comment is important.

MichaelG.

[JasonBModerator @jasonb]

As similar effect to the file Michael links to can be made by grinding the to flat faces off a hand file to just leave the cutting edge. I have a couple of files modified like this for squaring off slots for cotters and wedges.

[john carruthersParticipant @johncarruthers46255]

Maybe use two or three hacksaw blades together?

[HopperParticipant @hopper]

The largest flat file you can fit in the slot should do the job. Depending on the size of the job, that might be a 12" flat bastard file, or if its smaller a six inch warding file might do the job. If its smaller again, a flat Swiss file might work better. Hard to say without knowing the size of the job.

[BazyleParticipant @bazyle]

You said widen not lengthen. A standard technique in clockmaking for ensuring the edges of wheel spokes are true is as follows.

Grind the teeth off your hardened vice jaws so they can be used directly with only a sheet of paper to protect and help grip the work.
Set the work with the marked line indicating the edge of the new slot dead in line with the top of the jaws and at that level or initially a little out of sight below the jaw.
Now work away until the file hits the jaws. It will skid over the hardened jaw and not damage the file teeth because the hard surface against hard surface gets no penetration,
The ends have to be done with care but if you want a curved inside end you can make 'reverse' filing buttons with a hardened inside of the hole instead of outside but that would be very difficult to clamp in place.

[Adam McCulloughParticipant @adammccullough31948]

Thanks for the suggestions.
The job is the front headstock bearing housing of a small lathe – 1920s I believe. Think portass s-type. It has the single split type of gunmetal bearing, which someone has overtightened at some point, cracking the casting as I believe is quite common.
A specialist welder was able to repair the casting, but it has distorted sufficiently that the slit is no longer uniform. I want to make the slit a uniform width so I can closely fit a little slip of fibre, lead or similar before I rebore the housing.
I guess I want to finish the slit to about 1/8″ at most, and the faces are perhaps 1.1/2″ x 3/4″.
As I don’t have any other working machines and its not easy to transport the casting, I’d like to find a way to get it a good uniform width by hand.
A file with teeth only on one edge sounds like it might work.

[Adam McCulloughParticipant @adammccullough31948]

That file brochure is fascinating. I think perhaps I want an lp1171.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Adam McCullough on 01/05/2017 09:23:17:
Thanks for the suggestions.
The job is the front headstock bearing housing of a small lathe – 1920s I believe.

[…]

I guess I want to finish the slit to about 1/8" at most, and the faces are perhaps 1.1/2" x 3/4".

.

Then I will stick with my original guess

The LP1168 is 2mm thick; has one safe edge and is available in different cuts.

Used with care [and perhaps a protective layer of Kapton tape on one face] it should be ideal.

MichaelG.

.

Edit: My post crossed with yours, Adam … You may be right: it really depends on the shape of the distortion, and your preferred style of working.

Edited By Michael Gilligan on 01/05/2017 09:47:13

[KWILParticipant @kwil]

I think I would stabilise the gap by part filling with a loaded epoxy, just enough to hold the gap at the ends, rebore and then remove the epoxy. That way not a long filing job and not so tedious.

[DustyParticipant @dusty]

Split bearings of this type, should be shimmed anyway. I acknowledge that in most cases they are not, by shimming it prevents the over tightening and subsequent cracking you have found. The fit of the bearing is adjusted by the thickness of the shim, it should be an easy sliding fit in the slot and should be made from steel never fibre or other compressible material. Make your shim or packing piece a good push fit, if you need to tap it in it is too thick, bore and then ease the packing piece for the easy sliding fit this should give you a little adjustment on the fit of the bearing

[Adam McCulloughParticipant @adammccullough31948]

Dusty – yes, I want to ensure that the slit is packed as it should have been in the first place.

I'm told that the original packer for this particular lathe would probably have been hard cellulose fibre, although I have also heard of cases where lead, bronze, steel, cast iron and even dense hardwood were used from the factory for this application. I can well understand the logic behind making it from something incompressible and then adjusting the shim for fit – it does seem like this would be the correct way to do it.

A

[JonParticipant @jon]

Awkward one you will never ever file flat with a flat file, it needs a belly on it.
Limiting factor is the slot that's in and getting something in to start with I assuming 2mm wide.

If theres room could file downwards in to bearing opening using a pillar file 2mm thick. Easier to remove and true up runouts.
Whereas if run a 2mm thick flat file down lengthways it will bow the ends.

Even the best files are not straight, look down the length in the light to see the bow and use to good advantage. Or even bend the file whilst using it to create the bow and remove metal in specific areas.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Jon on 01/05/2017 15:11:54:

[a] Awkward one you will never ever file flat with a flat file, it needs a belly on it.

[…]

[b] If theres room could file downwards in to bearing opening using a pillar file 2mm thick. Easier to remove and true up runouts.

.

Jon,

I bow to your evident wisdom, but in practice, doesn't [a] presume that you can see the surface that you're filing ?

[genuine question … I would be grateful for your guidance]

MichaelG.

.

P.S. … [b] is what I had in mind when I suggested the LP1168 files.

[DustyParticipant @dusty]

The other way I have seen is to bore the bearing, then assemble it minus packing, adjust the fit of the bearing and then make the packer to fit the slot. The problem with that way is that you do need the slot to be parallel in order to measure the gap. A set of slip gauges is always useful when doing these sort of jobs. Mine came from a large internet auction site and cost not a lot. Imperial are generally cheaper than metric.

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