Source for a dovetail scraping reference?

rhb said:

I did a modest amount of scraping 20+ years ago to true up a small Chinese bandsaw. Scraping, hacksaw and files were my only option at the time. While not economic, the skill was worth the time spent. And the saw cuts true and will slice dime thickness pieces from bar stock.

For lack of practice, I have done a number of projects recently using files rather than my milling machine just to maintain the ability to use a file.

I bought a small lathe which I would like to scrape true and tune for precision work. Amazingly a 0.0001" indicator on the inside of the spindle taper does not move at slow speed. It increases a good bit when I speed it up, but I plan to address the imbalance by building a dynamic balancer and balancing the spindle plate. My assumption is that for precision work I'll use fixture plates or collets.

To scrape the dovetails I need a spotting reference. Is there an economical source for these or do I need to make my own?

If I need to make my own, what's the best material? I've got some ductile iron bar I can slice a slab off. That seems as if it would be the most stable material.

This is a warm up exercise for overhauling my Clausing lathe.

BTW I have a copy of Connelly. I've not read it in many years. But I did read it long ago.

Thanks,
Reg

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rhb said:

I just ordered 6" and 12" castings from Gary Martin and had a nice chat. I'm sure I'll get some longer ones, but these will do for getting started.

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rhb said:

Thanks to all. I couldn't find any castings for metrology items on Martin's website, but I'll email him.

I'd like to have some small spotting tools for the mini-lathe, however, I want larger tools for my larger machines. I'll be in touch by PM. I'll also take a scraper to my ductile iron bar and see what that's like. Scraping steel is tedious at best.

I'm trying to buy a copy of the publications by Moore Tool, but am having trouble reaching anyone. There are used copies of "Foundations of Mechanical Accuracy" on Amazon for $5000! Totally crazy. I had it once on interlibrary loan, but could never find a copy for sale. I very much hope that it is actually available from Moore.

With the forum moderator's indulgence I'd like to explain what I'm up to.

A small Schaublin or Hardinge toolroom lathe is either expensive or in need of a lot of work. And replacement parts are expensive and difficult to get. Chinese mini-lathes are partially machined casting kits for toolroom purposes. But parts are easy to get at reasonable prices. So if I make a mistake, it's not expensive. And I'll learn a lot more than buying a brand name toolroom lathe in good condition.

The big question I have at the moment is the spindle bearings. While I read less than 0.0001" TIR rotating it slowly, I have no idea if the bearing preload is correct. You can often make a poor bearing look good for a while by excessive preload. But it galls quickly. My Clausing lathe is a plain journal bearing. Those are pretty easy to understand and adjust. Ball and taper bearings are rather more involved. However, I have tooling to make any adjustment called for whether end play per air cooled VW practice or rotational drag per more modern practice.

To start with it seems to me I should remove the spindle, determine the size and type of bearings and then reassemble to specifications for comparable bearings from Torrington or similar. I've ordered MT 2, 3 & 4 test bars from India. The MT 4 is for my Clausing. Once I have those I can evaluate the stock bearings, alignment of the spindle taper, etc and purchase higher grade bearings if needed.

There is though a question as to whether a plain journal bearing would be more cost effective for the purpose of eliminating periodic spindle errors. Even if the stock bearings are poor, I should be able to grind between centers using a toolpost grinder a collar to press on the spindle. Once that is done, it's just a normal plain tapered journal job. My Clausing is rather worn, but I should be able to use it if needed.

So I'm very interested in opinions about roller bearings vs plain bearings for precision work.

As I only intend to use this for toolroom class work, the 3 jaw is pointless. So I plan to turn away the mounting plate from the spindle. All work will be done using collets or a fixture plate mounted on a drawbar MT 3 arbor. I had considered balancing it, but on consideration don't think it worth the trouble. However, I will build a dynamic balancer for use when setting up work on fixture plates.

As I am "reconditioning" a lathe, this seems the appropriate forum. I'm just working on a generic, no name machine that happens to be new. As I need it to make tooling for gauging precision RF connectors it is a convenient size and so long as I execute the work correctly should be as capable as any toolroom lathe of comparable size.

For reference, the connectors I'm concerned with have tolerance limits of 0.0002". Out of spec connectors can destroy the mating connector. Aside from often being difficult to replace because of the manner in which they are installed, they are also quite expensive. I'm not going to be using 1 mm series RF connectors, but those sell for $1000 each. The ones I'm using are generally under $200 for quality units.

Have Fun!
Reg

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dgfoster said:

I have a few of my 18” prism/straight edge/ levels in stock. They are cast in my foundry in grey iron 40 and are thermally stress relieved. They ship in a USPS flat rate box and are sold as a raw casting or machined.

Denis Foster 18" Straight Edge / Prism

Denis

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