# Best Way to Machine a prism for checking ways



## binnaway (Apr 30, 2013)

What is the best option to machine a prism so I can check the ways on a lathe and mill for hand scraping

Refards

Garry


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## 4GSR (May 1, 2013)

If you're talking about checking a vee way,  the simplest is taking a small vee block, setting it on top of the vee, upside down.  Either mike the thickness from the top of the vee block to the underside of the bed way, or measure the height from the top of the vee block to a flat spot on top of the bed.  This will give you a fairly accurate measurement within a couple of thousands.  It will at least tell you that your bed is worn in a given area, if you're lucky, no wear at all.

Now if you are wanting to make a "scraping iron" as I call them to scrape a vee to, I would suggest to talk to Richard about doing this.  My preference is to get the bed re-machined and work from this.

Ken


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## Richard King (May 1, 2013)

Ken is right, if you can get the bed ground or planned, you will be money and time ahead.  Scraping a lathe bed is a pain especially a SB with double Vee's.  There are several names for cart Iron straight-edges.  I use yo make all of them.  I prefer a camel back with a 45 deg side angle to do dovetails.  The triangle style will bend or conform to the way you scraping as they have no support.  

Many make the mistake in assuming you have to match fit the flat and dovetail at the same degree of angle with a 2 sided prism.  This is wrong as we scrape both flats first parallel to each other and then one dovetail and then measure and scrape the other dovetail parallel.  I will tip up a angled camel-back to do this.    Maybe you should tell us exactly what your planing on scraping, see we can give you the right answer.

Camel backs are also called hump backs.


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