Using Micrometer/Hi-Spot blue

[Keith Wilkinson 1Participant @keithwilkinson1]

Of course we are only touching the surface of the use of scrapin g ,we set up the basic machined bed casting with headstock base using a precision level ,we then scraped the (shears ) horizontal but of course our machines could not always be accommodated full length because of available space,we therefore scraped both ends of each piece of bed flat and square also the level of the jointing keys which wer levelled using a dial guage (It was a long time ago).We must not forget that on machines with uprights such as a vertical boring mill,or planer the uprights had to be vertical to the bed and to do this to the fine limits required they were scraped,and had to be scraped unevenly so as to counterany vertical misalignment.This was achieved by scraping one area more than others long before bed and surface finish were thought about .It was very skillfull as it was not econimical to keep lifting the uprights to the base to test if they were vertical, This was known to us as” throwing” the upright to vertical.Scrapinng of course was used in the alignment of the loose head stock also.

[RopetanglerParticipant @ropetangler]

Posted by Pat on 25/05/2011 21:03:13:

removing the high bright spots what are enclosed as islands in a blue sea.

 

Gordon if you rub the parts together the ‘blue’ accumulates in the gaps. Removing the bright spots will then take you further away from being flat not nearer. Some where along the line the spot contact and the rubbing methods have become mixed.

 

Regards – Pat

 

Hi All,

I am confused by the statement above. Sureley if you scrape away the high points, (which are the bright spots, because the bluing compound has accumulated in the low areas), then you are bringing the workpiece closer to being flat, not further away. On the other hand if you had blued your reference plate, and then lightly placed a smallish workpiece on it, with no wiggling or rubbing I could well imagine that the blue would only touch the high spots, and then you would scrape the blue points to improve the flatness.

Regards,

Rob

 

[Clive HartlandParticipant @clivehartland94829]

One item that I have found good for applying the blue is a wad of rolled up felt.

The type that the children use for making finger puppets I believe.

I roll it into a round shape about or less than 1″ and then bind with string.

It never wears and stays moist and you dont get blue fingers.

further to the mode of scraping, by sliding the item being scraped across the surface carrying the blue then the lighter areas are the highest. The darker areas are the hollows.

I do not try to achieve 100% coverage by scraping, this would defeat the object of scraping anyway. The idea is to get a flat surface with some surface mottling which will retain lubrication.

Any scraping patterns are purely cosmetic and may look good but do little for the purpose of scraping.

 

Clive

[DustyParticipant @dusty]

I have been pondering over this question since it was posted. The conclusion that I have come to is that two very different methods of bluing are being talked about.

The first, which is the method I was taught is that you have film of blue on the surface plate this should be translucent, in other words very thin. The workpiece is the rubbed onto the surface plate, just a couple of times. The blue will transfer to the high spots. These are then removed by scraper, file or what have you. This is repeated until you get an even pattern of blue spots over the surface.

The second method appears to use a much thicker film of blue which will accumulate in the low points of the workpiece. You then remove the bright areas.

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

What is the best shape for the cutting edge of the scraper and what is the best way of using one ?

 

This is not an idle question – the scrapers that I have used and seen used in industry and the ones described in various books and articles are many and varied both in design and in the way they are applied to the work .

 

The main variations of design are as regards the front rake angle (square across or a more obtuse angle) and the radius/shape of the cutting edge (in plan) .

 

The main variations in application are the angle of attack of scraper to work , whether to cut on push stroke , pull stroke or both and whether to use lubricant .

 

Further question is whether one design and method suffice for all purposes or are there roughing , fine cutting and frosting variants .

 

 

[Sub MandrelParticipant @submandrel]

I scraped the bracket that joins the column to the base of my X2 mill. When I started it was about 25% contact and there was a fore-aft error of over a thou, so I concentrated my scraping near the front. There were some hard patches that were probably the source of the original error as they stuck up above the machined surface.

 

I used stuart micrometer paste and the regularly honed side of a parting tool as a scraper. No fancy shapes. My skin turned blue and the endless re-assembly (to test the angle) and finger-pain turned the air blue as well.

 

But I did improve the verticallity of the standard and get about 75% contact, which made the mill noticeably more rigid.

 

Neil

[Keith Wilkinson 1Participant @keithwilkinson1]

We ashape and ground smooth then hardened and we ground them to a shallowV looking in profile.We lways had old files drawn out to a broad “Y”The drawn out edge was a slight radius and was sharpened on a Carborundum wheel not a grind stone.If there was a lot of material to remove a square profile carbon tipped scraper was used with an oblique edge,the same tool was always used for scraping steel.

Rough scraping is done using long curls like a letter c and each area is scraped from various directions when the final bed is starting to appear the long curls can be reduce to proper curling in small areas before finish curling ot mottling whichever is chosen.

Imagine a planing machine with 40 foot bed and a table in two pieces joined together.The bed has to be levelled and jointed before any scraping can begin and then the table jointed and scraped to the bed.The sheers (slides) were about 15 inches wide and there were 4 of them.It was a long tedious job but when completed gave much satisfaction.

 

[John McNamaraParticipant @johnmcnamara74883]

Hi All

For scraping I use Windsor and Newton Prussian Blue artists oil (not acrylic) colour. It is sold in different grades, it pays to pay a little more for the best quality, not student grade. A small tube will go a long way.

While you are at the artists supply shop pick up a small rubber print roller. Mine is about 25mm wide. (One that has good centered bearings or that will be your first job to rectify) otherwise it will not roll easily; the oil colour is very slippery on glass and you will get colour banding. I know that from experience. You also need a small glass plate.

The method is simple; put a tiny dot of oil on the glass and roll an even film out over the surface, as fine as needed. Then use the roller to transfer the colour to the work.  If the scraping is at the early stages you can use more. As it progresses you need less, the objective being the thinnest film possible. You may need to thin the colour with a little linseed oil. At the end of the day clean the glass and the roller for the next day.

The only difficulty arises when you can’t reach the work with the roller then I use my finger!

Near the end of the scraping you get to a point where the film of colour is too thick to work effectively. At that point rubbing the surface with methylated spirit may help it depends on the steel, if it goes dull you can then very slightly rub the surfaces together and you will get bright spots where they touch.

The bible for me is this book. One day as is the norm I was browsing at the back of a secondhand bookshop, I found a copy. As all will know in this place in ANY secondhand bookshop the engineering section is at the back of the shop on the lowest shelves If at all….Bah Humbug.

machine tool reconditioning by edward f. Connelly

Maybe your local library has a copy. I have seen it on Amazon.

Cheers
John

Edited By John McNamara on 06/07/2011 01:49:21

Edited By John McNamara on 06/07/2011 01:51:39

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