Ground Flat Stock Not Flat

[Steve CrowParticipant @stevecrow46066]

Sorry for this, yet another gauge plate question.

Thanks for all your previous advice, I've got my gauge plate and yes, it saws and files beautifully.

It's 5mm x 30mm and I cut of a piece 13" long to make the base of a jig.

When I put it on my surface plate, there was a noticeable bend to it. Concave side down, I could stick a 0.20 mm slip gauge under it.

It doesn't sound much, but it's enough to feel a rocking motion when concave side up.

Is this normal?

I presume that when gauge plate is ground, its held on a magnetic table but it must spring to its natural state when released?

Any thoughts?

Cheers

Steve

[Steve CrowParticipant @stevecrow46066]

[Neil WyattModerator @neilwyatt]

<siri voice> I'm sorry I can't answer that but I found this on the web: </siri voice>

How flat is Ground Flat Stock / Gauge Plate?

Unfortunately there is no real definitive flatness tolerance. The “flat” in ground flat stock purely means its not round. Flatness depends on thickness, 1mm thick material is difficult to make as it is so thin thus more susceptible to bowing. Thicker sizes tend to be more stable. An acceptable tolerance would be 1mm in 1000mm long. If you require a specific flatness tolerance email or call us to discuss this possibility.

http://www.coventry-grinders.co.uk/faqs/

[Chris Evans 6Participant @chrisevans6]

As Neil has shown above it is the nature of the material, I doubt you would get better flatness unless you go over 10/12mm. In my working life I used hundreds of pieces of Ground Flat Stock, it takes a lot of patience on a surface grinder with fag paper and baking foil for shimming with the magnetic table barely on to get thin material flat.

[Richard S2Participant @richards2]

I've seen and used good tolerance material and some not so good. These days, it depends where it comes from and what you choose to pay.

A UK company offers AISI O1 (WI.2510) ground flat stock spec quoted as a flatness of 0.2mm per 500mm in their range ……………….A piece of 2mm x 200 x 500mm 'aint cheap though!….(these days) .

[EmgeeParticipant @emgee]

Steve,

if ater machining you intend to heat treat to harden for your jig you may find even more distortion. You really need to start with an oversize thickness to allow for grinding "flat" to thickness after hardening.

Emgee

[Neil LickfoldParticipant @neillickfold44316]

The gauge plate that we buy is flat to less than 0.03mm in general. So when a part is made, it is heat treated It can be ground and be at the nominal size in most cases. Sometimes it goes .02mm or .03mm undersize, but in our case the thickness of this part is not critical. We make these blades from 1/8 stock, 6mm 8mm and 10mm from 2inch wide to 100mm wide. It is O1 oil quenched tool steel.

Neil

[HopperParticipant @hopper]

Posted by Neil Wyatt on 18/02/2017 18:50:51:

I'm sorry I can't answer that but I found this on the web:

How flat is Ground Flat Stock / Gauge Plate?

… An acceptable tolerance would be 1mm in 1000mm long….

Crikey. One in a thousand. That's 12 thou per foot. That's a tapered wedge!

So much for the myths of scraping bed ways etc in to pieces of gauge plate in lieu of proper surface plates and straight edges.

I reckon I have pieces of ordinary bright mild steel that are flatter than 12 thou per foot.

Edited By Hopper on 18/02/2017 23:48:54

[Tony Pratt 1Participant @tonypratt1]

Posted by Hopper on 18/02/2017 23:48:07:

Posted by Neil Wyatt on 18/02/2017 18:50:51:

I'm sorry I can't answer that but I found this on the web:

How flat is Ground Flat Stock / Gauge Plate?

… An acceptable tolerance would be 1mm in 1000mm long….

Crikey. One in a thousand. That's 12 thou per foot. That's a tapered wedge!

I reckon I have pieces of ordinary bright mild steel that are flatter than 12 thou per foot.

Edited By Hopper on 18/02/2017 23:48:54

They are talking about how straight the material is not how parallel, so not wedge like.

Tony

 

Edited By Tony Pratt 1 on 19/02/2017 08:56:17

Edited By Tony Pratt 1 on 19/02/2017 08:56:42

[Tony Pratt 1Participant @tonypratt1]

Any idea why the font is so small on my previous post?

Edited By Tony Pratt 1 on 19/02/2017 08:57:52

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Tony Pratt 1 on 19/02/2017 08:57:07:

Any idea why the font is so small on my previous post?

Edited By Tony Pratt 1 on 19/02/2017 08:57:52

.

Because you continued within the post from Hopper, which he had edited.

… font size reduces for the 'Edited By' footnote.

MichaelG.

[Frances IoMParticipant @francesiom58905]

it’s small because you placed your comment as part of Hopper’s quote which had set a small font to indicate he had edited it.

[Tony Pratt 1Participant @tonypratt1]

Thanks Michael G & Frances,

Tony

[Neil WyattModerator @neilwyatt]

If accidentally delete the empty line inserted below a quote, you can hover the mouse near the bottom or top of a quote a red 'return' symbol will appear letting you insert a new paragraph.

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