Author Topic: Gib Strip for a Capco Surface Grinder  (Read 536 times)

Offline philf

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Gib Strip for a Capco Surface Grinder
« on: May 25, 2017, 01:30:49 PM »
I recently bought a bargain Capco surface grinder aptly described as a project.

There were many bits missing or not quite right but most could easily be made (and mostly have been).

The one part I'm having difficulty with is the gib strip for the main slide which was missing.

It's 640mm long, 9.5mm thick with 55 degree angles.

If I start with 1" x 3/8" cold rolled mild steel it'll no doubt ending up like a banana when I machine 1 of the 55 degree angles.

I thought of taking off a very small amount on one side and then the other to try to balance things out but this will take forever. My angled vice has only 4" jaws so any machining will be have to be in 5 or 6 steps.

Hot rolled steel might distort less but will require the sliding face machining and I'm limited to 300mm travel so again I can't do it in one go.

Anyone got any bright ideas?

Cheers.

Phil.
Phil Fern
Location: Marple, Cheshire

Offline PekkaNF

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Re: Gib Strip for a Capco Surface Grinder
« Reply #1 on: May 25, 2017, 02:27:52 PM »
Gib can be banana when it is that slender. But the cross section must stay constant. My friend just ordered spare for one milling machine and spent two weekends scraping it.

Can you use the grinder table (bolt it onto milling machine table) and use that as a jig to mill the gib? If you clock the "jig" or table straight you can move the gib, clamp it against the dovetail and mill the top with endmill with reasonable accuracy.

I wonder if I can explain it right: You size the stock to right flatness, then you have a square bit. Then you clamp this square stock into the dovetail using roll pin or whatever means necessary. Now you are offereing it to the end mill at correct angle, because it is in the dovetail in situ. You mill the top straight (it will be proud of the dovetail, because you have unwanted corner at the bottom), then you shim bottom at the dovetail, put this gib strip atop of the shim, clamp, and mill this other side. I may need to resor drawing (suck at it).

I would not use any type of tilting vice on this long/slender piece. You will be fighting a lit to get the setup repeatable.

Pekka
« Last Edit: May 25, 2017, 04:43:08 PM by PekkaNF »

Offline Pete.

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Re: Gib Strip for a Capco Surface Grinder
« Reply #2 on: May 25, 2017, 03:17:53 PM »
Just buy the 3/8 cold rolled strip, mill the angles, scrape the working face for oil pockets and fit it. I did this on a lathe recently and it worked out fine.

Offline philf

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Re: Gib Strip for a Capco Surface Grinder
« Reply #3 on: May 26, 2017, 01:30:50 PM »
Thanks Pekka and Pete,

I'll go down the cold rolled steel route. If it fails it won't have cost much.

Bolting the grinder table to the mill isn't easy as the grinder table is bigger so, unless I drill holes in the grinder table, I cant' get to any T-slots to hold it down.

I have a smaller table off another machine with 55 degree dovetails - I may try to clamp the gib to that.

Whatever - it'll have to wait a few days as my wife and I are off on our bikes for a few days - hope it cools down a bit!

Cheers.

Phil.
Phil Fern
Location: Marple, Cheshire

Offline Pete.

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Re: Gib Strip for a Capco Surface Grinder
« Reply #4 on: May 26, 2017, 01:40:36 PM »
If it's not a tapered gib then it must be screw and locknut. There's no reason at all why you couldn't make it in two halves.

Offline philf

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Re: Gib Strip for a Capco Surface Grinder
« Reply #5 on: May 27, 2017, 04:43:28 AM »
If it's not a tapered gib then it must be screw and locknut. There's no reason at all why you couldn't make it in two halves.

Hi Pete,

A good idea  :thumbup: - or so I thought until I just checked the machine.

The travel is so long that one half of the gib would fall out as you were quite a way from the limit.  :(

Cheers.

Phil.
Phil Fern
Location: Marple, Cheshire

Offline Pete.

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Re: Gib Strip for a Capco Surface Grinder
« Reply #6 on: May 27, 2017, 05:08:55 AM »
Well, to be honest the top and bottom angled faces don't need to be bob-on accurate since they do no work. If you made it in one piece you could cut the bevels in multiple set-ups.

Offline PekkaNF

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Re: Gib Strip for a Capco Surface Grinder
« Reply #7 on: May 27, 2017, 07:03:49 AM »
IMHO three sufaces has to be pretty good on traditional non tapered gib strip, when it wears and the screw holes oval you don't want it all over the slot.

There are several choices, I still haven't made up my mind...even after readin old brittish poets like Geo H. Thomas et.al.
http://lh5.ggpht.com/_ozT1G3WqXg4/TUqsPuzQqeI/AAAAAAAALKM/HweM0rgDKQU/s800/gib.jpg

Pekka

Offline philf

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Re: Gib Strip for a Capco Surface Grinder
« Reply #8 on: June 09, 2017, 05:06:39 PM »
I finally got round to picking up a nice flat piece of cold rolled 1" x 3/8" MS yesterday.

I decided the best way of machining the gib without ending up with a banana was to make a fixture to clamp the gib to and to machine equal amounts off both sides a bit at a time.



The clamping screws are a good fit in the fixture to minimise movement. I decided to do the machining in 4 160mm sections as the vice only has 4" jaws and didn't want too much overhanging.

Here's the gib with all its tapped holes and the fixture clamped in the first position. I think this is the first time I've used the angled vice.



Here's the end view after taking off approx 6mm on both sides (3 passes of 2mm each side).



With a bit of deburring with a file the gib looks good and has stayed quite flat.

Even though I think it will work as-is I'll probably try to scrape it before drilling and reaming a couple of location dowels. The adjusting screws push on rods angled to match the gib.

Phil.
« Last Edit: July 13, 2017, 12:54:18 PM by philf »
Phil Fern
Location: Marple, Cheshire