Cast Iron Bar for Making a Precision Straight Edge

[billf]

I need a 44” long, precision straight edge with a 50 degree bevel for marking and scraping the dovetail ways on a Bridgeport Series 1 mill that I am going recondition. Since I cannot find one to purchase, I am going to make my own from a grey cast iron bar. Can anyone suggest a supplier for a stress relieved cast iron bar suitable for this task?

[TGTool]

Michael Morgan had been supplying castings for same, and someone on the Practical Machinist site had been as well. It's a camelback with the bevel on one edge so would be a better head start than a straight bar which would not be nearly as rigid.

[thistle]

Stephen Thomas of PM might have some straight edge castings in stock, other wise you might try Craig Donges.

[billf]

How do I get in touch with Michael Morgan, Stephen Thomas, and Craig Donges? I am new to Practical Machinist. Is there some way to contact them through PM? Thank you for your replies.

[TGTool]

Try www.machinerepair.com for Michael Morgan. He also suggests checking with The Challenge Machinery Company, 1433 Fulton Street, Grand Haven, MI 49417-1594, (616) 842-6665.

At PracticalMachinist.com you should be able to turn up private message and/or email links for their members. You may have to register to use those features, I don't remember.

[Oldbrock]

Craig Donges
E-mail Address(es):
windmillguyinohio@yahoo.com His castings are second to none, Peter

[Mcgyver]

Try www.machinerepair.com for Michael Morgan. He also suggests checking with The Challenge Machinery Company, 1433 Fulton Street, Grand Haven, MI 49417-1594, (616) 842-6665.

at that size you are into expensive stuff....I've a Challenge 60" (can barely carry it) it and iirc it lists at 1500 or something. Stephen Thomas's camel back is neat in that one side is made with an acute angle to get into the dovetails but it is no where near 44"

If you can find stress relieved CI, just get a suitable piece of grey iron durabar and then find somewhere to have it stress relieved - nearest heat treat shop. It might be easier to find these things separately rather than under one roof - if you're at some distance have the durabar dropped shipped to the heat treater. Next, I would go maybe 30 or 36 - they become more challenging to handle and you can step it along - ie do 30" then with a 50% overlap do the last 14

Lastly, you only need it more acute than the dovetail; if you found a 50 or 45 degree it would be just as good and there's no need to scrape more than one face. Where its handy to have the angle dead on with two faces scraped is when the dovetails are so small its hard to get the reference to sit flat on it....not the case with a full sized mill and any any event you only spot one surface at a time

[4GSR]

I have a piece of durabar G-2 gray iron I purchased over ten years ago. Been sitting out in the Texas hot sun for almost 6 years now. One of these days, I have plans to make a straightedge out of it.

Ken

[Forrest Addy]

Well, first of all, it may be nice to have a straightedge equal in length for the work you wish to put it to but such is not the case most of the time. You will most likely settle for a 36" or a 48" straight edge because they seem to come in foot increments. I can strongly reccommend the 32" straighedges Steven Thomas designed. It was made specfically for re-conditioning turret mills. 32" may seem short for a 42" table but by employing only a little care with the overlap, longer surfaces can be printed very satisfactorily with tooling of less than full length.

I see you specify a 50 degree angle. You will probably get better results from a dovetail straight edge whose angle a bit more acute than the DT you are re-scraping. You never use a dovetail straight edge for angle setting when re-scraping. You teeter the flat on a piece of soft shim to fit the angle into the dovetail but only to check for straightness, not angle. You keep the angle aother way.

In re-scraping you need to use as much of the original geometry as possible. Every bit of extra metal you have to scrape off takes extra time and requires more even more time to scrape the mating part to fit it. The first thing you do after the survey, cleaning and prepping for scraping ect is to make a short block for each dovetail angle scraped to fit where it's not worn - usually near the ends of travel.

Use these blocks (be sure to identify them - dovetails angle can vary on the same machine) to prove the dovetail angles as you scrape. You often have several references going at the same time and you scrape according to what the readings of these references tell you.

Regardless of what you hear, do NOT blindly scrape to a dovetail straight edge unless it has been scraped and calibrated to the angle you are scraping for restoration.

You will probably find the table to to be a little convex and the table ways on the table concave; parallel to the table top minus a bit for the wear in the center. The saddle ways on the knee will be worn hollow. The column ways may show little wear because they take little weight load - only the incidental loads of cutting and guidance of the knee. These are well known wear patterns and your machine will more or less duplicate these conditions. Connelly's RMT offers the order and sequence of the work in restoring a machine like yours to like new condition, alignment, and accuracy.

Your wife will rejoice. You won't be out with the boys if you hope to complete this re-scraping project in less than a year of evenings and week-ends.

Good Luck.

[lazlo]

I've a Challenge 60" (can barely carry it) it and iirc it lists at 1500 or something.

How do you know it's flat? If you bought it used, it's probably not