24 x 36 cast iron surface plate - qualifying

[matt_isserstedt]

I've been hoping this forum would open...I have in my shop a 24 x 36 Challenge Machinery cast iron surface plate. It sits on a 4 legged stand actually on the 3 points (I welded flat washers to the frame to better locate the 3 legs), and up to now its basically a storage surface for CNC tools and projects. Its in good condition, with uniform scraping marks like a pro would do...suspect original from Challenge and I have rust protected it fairly well. So I'd be worried about movement of the iron due to stresses, or whatever it went thru in its former life.

I have a lifting bridle and the two steel pivot pegs, so potentially it could be inverted. HOWever, I have it boxed into the shop in a pretty good way...lets just say I'd have to move my VMC at this point to extract the plate from the shop. Its not impossible, but would be a fair amount of work.

So I'm trying to figure out what I should do at this point, to qualify this as a master I could use.

Options for inspection, and possible correction (if needed) are

1. remove from shop, take somewhere else to spot and scrape with a shop crane to go along for support. This would require someone else close willing to let me work there and with a granite plate they trusted me to work with. I haven't met that person yet.

2. hire a plate calibration company to inspect, I suppose I'd have to scrape rather than them lapping it like granite. But that could take a lot of their time depending on how far its out. I don't think reliable contact could be achieved as it would seem like shooting in the dark somewhat.

3. I have a 199Z master level, initial thoughts were to use this tool to take a survey, basically moving it all over and keeping notes of the movements to establish high spots, and possibly spots I should avoid. I also have a 2ft and a 4ft straightedge, one camelback and one dovetailed, which could also be qualified elsewhere more easily. Wondering if there's a combination of level and straight I could use to make any correction if needed without going counter productive.

4...???...

Sorry I don't have any actual numbers or preliminary work to report, yet. My "other plate" meaning my life is full with things for the moment but its been in the back of my head and I was trying to sort out my plan of attack (also waiting for yellow ink to come into stock locally...its on backorder at present)

Thanks in advance for your advice

 

[CBlair]

Matt what little I have read usually states to get a flat plane you scrape three plates together as they cancel the errors out. Of course that may just be for when they are first made. I would guess that as often as people use granite plates that the same measuring procedure for them would work for your plate.

But then that is why we have this subforum, we can hopefully get people with actual experience to answer instead of us guessers.

Charles

 

[sfriedberg]

Hopefully, one of the pros will comment on this. I have done enough reading to know that your plate can definitely be surveyed in-situ for discrepancies from a true plane using gizmos like a Planekator or an auto-collimator, although they'd probably prefer access all the way around the plate, so if it's wedged into a corner or an alcove that's a nuisance. With a quantitative survey for high and low spots, and a smaller, easier-to-manage surface plate, you can improve the Challenge plate condition.

 

[Richard King]

If it was my plate I would get it out of the shop some how. Possibly get a bunch of buddies who have strong backs, rig it to a I beam or use some oak 4 x 4's and strap it up to it and lift it out of the hole it's by craddleing it some how. Or get something like a transmission jack on wheels and after you have it out of there call around and see if you can find a shop with the granite plate with a jib crane. Maybe you can barter with them to check your CI plate on their granite. If not buy a granite plate or rent one from a local used machine dealer. Hopefully there will be a sticker on it and it;s a A grade or better and was inspected lately. You can use a level, a straight-egde and 1-2-3 blocks like we did at the Kalamazoo class and "map" the plate, but that will take 2 or 3 times longer to inspect it and then scrape it. There are several ways to check it, but lap scrapng with a smaller plate and straight-edge is a slow way, not to say it can'tbe done that way, but you know it would be a pain doing it that way. Same with the 3 plate method. You may want to call Challenge and see what they would charge you to scrape it. Challenge Precision|Workholding|Angle Plates|Lapping Plates|Precision Manufacturing I had heard they closed, but maybe they are still open Rich

 

[D.Brown]

I suppose I'd have to scrape rather than them lapping it like granite.

It can be flattened/trued with a lapping plate.

 

[Richard King]

I had to show you these You Tube video's Jan made. You need to check him out on the net "Jan Sverre Haugjord"· He is helping and hosting the Norway class and assisting me at the Swedish class. He took the 5 day GA class in 2013 and he has become what I call a "Natural" scraper. He is doing what I ask all my students to do. Teach! He is scraping a plate that he needs to scrape his Mill column. The first one he shot and sent to me, I emailed him a Trick he shows in the 2nd one and then he uses the plate in the 3rd one. He has several You-Tubes showing scraping a SE and the rebuilding of his Mill. Enjoy. Thanks Jan for the good show and great scraping, I am very proud of my students. Rich

https://www.youtube.com/watch?v=O2nyrSq0tY4 Plate scraping
https://www.youtube.com/watch?v=NzxfycWSSCs Plate lifting trick and sharpening the blade
https://www.youtube.com/watch?v=XIx67K4hG6Q Usuing the finished plate on the column of his mill

 

[Ocean]

Nice videos, Jan's doing a truly professional job.

With that said, it's easy to scrape old CI plates for flatness when you have a gigantic granite plate like the one Jan shows in his videos!