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Flat Gib Strips - advice

Lurk

Cast Iron
Joined
Feb 10, 2014
Location
Peak District UK
Appreciate this is once again a pretty basic question - but here goes.

The original flat gib strip from the tool slide on my shaper was 0.900 x 0.125 x 10" long and had a real good kink part way down and pretty badly scored & rusted up. I tried peening it and concluded it was time to renew after I was unable to make it much better.

My first mistake was selecting a length of 0.250" thick x 1" Bright Steel (Mild Steel) - I machined the same amount of each side of the strip with my shaper and it still sprung & twisted. - After a couple of attempts to peen it flat it remains twisted along its length - I got it to within a few thou' and concluded I was fighting a losing battle.

So next attempt is with some gauge plate pre ground to 0.125" thick. Only a small strip but expensive as such and I suspect overkill.

The question is - what material would normally be used for such Gib strips - running as it is on Cast Iron dovetails.

Should the ground surface be 'flaked' or left as is ? I was looking to flake only the fixed portion of the dovetail as its always covered. Ive held back in the knowledge that I shouldn't flake both faces (Gib & Fixed section).

Thoughts ?
Mat:nutter:
 
Do you have Durabar or a similar product in the UK? It's just cast iron bar stock. That's what I would use.

You could use steel if you have to, but mild steel is generally a poor bearing material, and it's harder to scrape and machine flat (as you have seen). Lot's of CNC machines have steel gibs with turcite on the bearing side. However, the tool slide on a shaper usually has a lock, and the lock probably won't work with Turcite.
 
Flat gib is usually not a big issue. It is just flat strip, generally mild steel, and is adjusted with a row of screws. Basically a cheap gib, maybe surface ground, never scraped that I have ever seen, although it would make sense to flake it for oil retention. Some fairly aggressive flaking before surface grinding could be good, and might be done with a die grinder, as opposed to a "real" scraper.. The surface grinding would bring the surface down to whatever depth of "flaking" is wanted.

Twisted gib strip would be bad, but a bow in the material is not a killer, since the screws tend to hold it flat against the other surface.

While I have heard of people using CI for them, the forces on it seem to be such as to threaten to crack it, so i would suppose a less brittle material such as mild steel is better. I have used mild steel, and even brass,
 
many a long thin part is shimmed on a mill or surface grinder in its relaxed state clamped without distorting its relaxed shape them machined
.
basically you got a twist banana shape part you dont beat it flat or let magnetic vise twist it flat. you got to hold it in its twist banana shape then machine it flat. some stuff need stress relieving or annealing often
.
i have seen stainless you can clamp it in banana shape mill a .030 bow out of it and as soon as vise unclamped again it bows again .015
.
quite often it takes many light cuts to get it all out. worst part is machining it flat and 24 hours later it warps again. its got to have time to think about warping
.
some parts gets sent to heat treat multiple times to anneal for example before AND after milling it is annealed so grinder has less problems with warpage
 
many a long thin part is shimmed on a mill or surface grinder in its relaxed state clamped without distorting its relaxed shape them machined
.
basically you got a twist banana shape part you dont beat it flat or let magnetic vise twist it flat. you got to hold it in its twist banana shape then machine it flat. some stuff need stress relieving or annealing often
.
i have seen stainless you can clamp it in banana shape mill a .030 bow out of it and as soon as vise unclamped again it bows again .015
.
quite often it takes many light cuts to get it all out. worst part is machining it flat and 24 hours later it warps again. its got to have time to think about warping
.
some parts gets sent to heat treat multiple times to anneal for example before AND after milling it is annealed so grinder has less problems with warpage

I figured I had it wrong trying to get it flat by 'just machining both sides equally. Bow I could understand but the twist ... took me back to making Oak cabinets and trying to get English Oak to stay flat - often leaving the timber part machined for a few weeks.

I think I will work on the gauge plate.

Thanks for the advice folks.
 
The trick with mild steel and cast iron bar in the sizes needed for gibs is to normalize it before machining it. Take it up to a good red heat for half an hour and let it cool down out of any drafts. It'll move a lot less after that.

Gauge plate is horrible stuff to make gibs from. It's O1 steel, which is a poor bearing material and the surface finish is bad (mirror finish is bad, in this instance). It's also not nice to scrape.
 








 
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