I have a lathe that I would like to scrape to a fairly high accuracy. Does anybody know of a good place to find cast iron straight edges, which are used to mark the bearing surfaces for scraping?

I am happy to find a rough casting and hand scrape it myself.

I guess I could also just jb-weld two steel bars into a 'T' and scrape the marking surface flat. I have a surface plate.

Thanks for any advice.

MSC industrial supply out of NY used to carry both iron and granite. www.mscdirect.com is their online site.

SPI used to offer iron parallels/straightedges too, back in the 80's. Haven't kept up with them though so don't know what their current product line is like, or if they even still exist ;)



Tiger

Search the net really good! I seem to remember a small outfit that makes them. You could of course check with Brown & Sharp as they use to make them.

Sad as it may sound though you may have to have the castings made yourself. Not a totally bad idea but it takes awhile for the castings to stabilize.

Another option is cast iron shapes available from MSC, McMaster-Carr and others. Yeah a bit of work here too and they are not the equal of hump back units, still a good way to make smaller straight edges.

Another option that you really should consider is antique shops. You will be surprised what you can find in these places. Further if you talk to the right shop you might bet a reference to a person in your area that specializes in tools. Probably not the most cost effective way to go about purchasing such hardware, but you might get lucky. The other thing to do is to never miss a local auction that is the result of a machine shop closeout.

Thanks
Dave

http://machinerepair.com/scrapers.html

see also http://www.cnczone.com/forums/showthread.php?t=11874&page=2

for a pic of some home made straight edges that are dead on - although for $200 for the casting you can't go wrong!

Thanks guys for the info. On another thread, The book 'Machine Tool Reconditioning and the Art of Hand Scraping' was mentioned. I bought it and I feel it was worth every penny of the $100+ I spent. The chapter on gib contruction and fitting alone was worth the price, imo.

Connelly, the author, spends many pages telling you how to make your own precision straight edges, parallels, and gauges. A very inspiring book. With the knowledge presented in this book, one can make many of the precision items, which are out of the price range of a hobbyist or small businessman.

Mcgyver, I would not recommend the machinerepair.com site to anyone. If my memory of the date is correct, in the spring of 2004, I sent a check for the video and book he advertises. The products were never sent. Several emails from me were never answered. Mike, or whoever runs this business, had it together enough to take my check to the bank and cash it before I could cancel it, however. I have been stuck for years on the issue of scraping until hearing about the Connelly book from you guys. Stay away from machinerepair.com!!

In order to recondition the lathe I have and build a cnc gantry mill, I would like to have a 4 foot long precision parallel/straight edge. Using this tool and a precision level, I think I will be able to get very accurate alignment of the ways of any mill or lathe.
I would like to try and make one myself out of a 49" long steel 'I' beam that I bought for $15. It is about 3" tall and 2" wide. In order to reenforce it, I want to 'cold weld,' with 'jb weld' or some other tough epoxy, vertical braces and diagonal braces. Once the braces are cut and glued in, I will have the beam ground on all four sides at a grinding company. Then, using a 30" on-the-diagonal surface plate that I have, I will touch up it's accuracy by hand scraping.
I am also thinking of beefing up the top and bottom surfaces with gray iron or steel plates, which would be cold welded to the beam using epoxy. I would then have it ground.
Do you think this will be stable enough to hold its accuracy? My feeling is that welding the braces by normal means will induce warping and stresses into the beam, making it very inaccurate. But I am wondering what differences in room temperature will do to the way epoxy pastes expand and contract. Maybe that will also make it very inaccurate.
Any thoughts?

never dealt with those guys at machinerepair , just saw they were advertising what you wanted, doesn't sound like i'd want to. I guess by the steel i beam idea you didn't find another source?

as far as the i beam goes, i wouldn't make it from steel, too much movement. get a piece of cast iron. Too much work goes into making a reference flat to have it move which steel will do. even if you get it normalized its my understanding that the CI crystalline structure is more stable.

here's a shot of some homemade ones. the completely blue against a camel back and are as good as anything by Browne & Sharpe, etc. they are about 24"

http://i20.photobucket.com/albums/b201/michael0100/scraping/homemadereferences.jpg

Mcgyver,
I think I will follow your advice and stay away from the steel I beam.

What do you think about getting three pieces of 2x1x36 or 48 gray iron rectagle and cold welding them together with epoxy into an I beam configuration? Or taking two iron strips and glueing 2x1 risers between them every 6 inches or so?

I am also interested in using standard dovetail ways for all of the axis in my router mill and scraping them to accurate alignment. Is friction the main issue in choosing ball bearing guide rails over standard metal-against-metal bearing surfaces? Can one just use stronger stepper motors and larger leadscrews to overcome any increase in friction?

I am also intrested in using an air powered roto-sander with 120-180 grit disks to rough in the bearing surfaces of workpieces that I am flattening until there is enough contact with the reference surface plate or parallel to warrant hand scraping. Is this method used? Is it hard to control?

you're wading out past area's I have experience with, so what I have to so say is more speculative than knowledge based....

that is one massive reference you're trying to build. I'd be concerned about its weight, both from a usability and distorting under its own weight. I'd be looking to either build something more modest like I posted above (which is a still very substantial), find an old camelback somehow (dealers, ebay etc) or buy a casting or buy a new one. don't know how much of an option the last two are, but big pieces of CI like you are describing are not cheap. I also don't know if there is any way to attach them that will be as rigid as a one piece casting. The Connelly book probably goes into depth on this, but do you need a 4' reference to scrape a 4' surface? I'd be inclined to use a 2-2.5 foot reference and overlap it.

the engineers here probably have more to say on this, but imo ball slides are a compromise over dovetails for a mill or lathe (metalworking). The have the advantage of an out of the box fit and accuracy (think of the effort to make from CI dovetails from scratch!) and low friction, but the bearing surfaces are so much smaller. maybe the industry guys can confirm, most industrial machines I’ve seen use a solid bearing surface like a dovetail for heavy machines.

were I building from scratch something with only a light cutting load, it would linear bearings. If possible, I'd prefer to build by restoration of a machine tool; I think it would be superior to use properly scraped dovetails as the bearing surface with more umph to over come the friction. that friction and inertial of the big casting is also your friend, ie climb milling.

to your last point, I'd be using a file before a portable grinder or sander. there's just no control with those things and who wants the grit everywhere. the tool you need is a power scraper, don't know if you can find a place that rents them as they're expensive, but makes short work of roughing.

I tried to made a straight egde from and I beam. I did not work. Everytime I machined a surface, it would twist from the stress. Even taking .005" off a surface caused it to go out of wack.

Vince

Again, thanks guys for the comments. I will difinitely stay away from making straight edges out of steel.

I will also attempt a more modest size to experiment with, considering the cost of materials and the time involved with scraping.

I think I will try making a 36" straight edge by epoxy welding two 1x2 gray iron strips into a 'T'. Then, I will get all sides ground and hand scrape to finish.

Also, is it inevitable that some deeper scratches will show up on the surface of the workpiece when scraping? I am able to get the workpiece surface to that shimmery, smooth look; but, when I look at it from a certain direction, I notice some deeper scratches.

dfro You can get about any grade of grey or ductile iron from Dura-Bar, make it the way you prefer. ( www.dura-bar.com)
RZ

What about getting some granite cutoff's from the local countertop place. You could then level it with something like moglice. Just an idea.

You can also get rough cast sections from MSC and McMaster-Carr. Not cheap though. You can also try Carr-Lane for castiron sections, unfortuantely they don't have anything precisely designed for what you want. You could produce servicable straight edges with some of their parts. The box section might be handy in shorter lengths.

There are certainly other sources for castiron sections. The biggest problem is you don't know if the parts have been seasoned. None of them are really optimal for the intended usage either. Surprisingly it is almost impossible to find anything on the net. You could find a local foundry and see if they will cast up what you need. You have to hope they have a pattern around otherwise you become a pattern maker.

Thanks
Dave

These days large straight edges are made of granite. They are more temperature stable and don't need as much care as the cast iron ones.