What type of Cast Iron is best suitable for dovetail slides

[Mark RandParticipant @markrand96270]

Aha, you'll want Whitworth Hex bar.

[IanTParticipant @iant]

That would be the simplest solution Mark – but I only had the six sided type in stock…

[Joseph Noci 1Participant @josephnoci1]

Hi Ian. Yes, I had considered just angling the block on the mill – the issue is that I hope to leave the lower half of the casting's dovetails in place ( see my sketches on the photos in the earlier part of these posts), as they are good and quite strong. Adding a separately machined dovetail block to butt/mate with that will never result in the new and old dovetails actually lining up. So the idea was to dovetail them together with the final cut skimming both old and new. I suppose I could simply machine away all the old dovetail section, and fit a full length new block, but I fear that that will weaken the main casting a lot.

Whatever the solution, it is going to be circuitous, a compromise, iffy, and a pain.

I guess I now have enough ideas from all who joined in, and now need to get to it!

Thanks

Joe

[HopperParticipant @hopper]

I agree with Neil's concerns about the piece splitting at the screw holes, or shearing the screws under extreme load or after extended use. It might be possible to make the insert piece a "double dovetail" shape instead of straight sided. So the insert would be slid down into position from the top, with the reverse dovetails machined into the head taking the load and the screws merely providing positive location in the vertical direction. A bit of extra work but a very solid construction, i would think. Just a thought.

[John OlsenParticipant @johnolsen79199]

There shouldn't actually be any extreme loads, unless he has another crash, in which case it might be better for this repair to fail rather than some other part that is still good. In other words, I would not want to make it too much stronger than the original. On the other hand, the double dovetail does sound quite elegant.

It is rather a pity that this is his only shaper, since 55 degrees is quite easy to do by just offsetting the head.

If you need any measurements taken from my one, I would be happy to help.

John

[Neil WyattModerator @neilwyatt]

It should be possible to jury-rig some form of toolholder that would function well enough to allow the shaper to make a new dovetail.

[Malcolm Foster 1Participant @malcolmfoster1]

Hi Guys, Thanks for the suggestions here in producing a dovetail, or in my case, the gib for one. Quite a coincidence as I am currently advertising my little horizontal mill on here and on Ebay. As I state there, all I can find wrong is a broken gib?, fractured in 3 places where the fixing screw holes are, which to me indicates it is cast iron, not steel, especially looking at the grain structure. Strange really as the Z-axis dovetail is machined in the C.I. base/stand and I would have anticipated using to different materials in such sliding contact.

I did wonder if a high-tech plastic would be better – unavailable in 1941! There is a little jacking screw protruding on the opposite side so it looks someone has overtightened against that to break the angled strip. The slide still functions well though.

If it does not go and I decide to keep it, I will have a go at making one on the mill or my lathe which, tbh, I had not considered.

Cheers,

Malcolm

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