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+--- Thread: mini mill (/thread-601.html)
RE: mini mill - Rickabilly - 07-17-2012
I haven't had a chance to sketch it up yet but when you see how it is supposed to be done you'll probably raise an eyebrow as it seems a bit wrong, or at least it did to me. as it is the only fine hand finishing tool that it pays to leave some of the rough grinding marks on, I'll get the sketches up tomorrow.
Best Regards
Rick
RE: mini mill - Mayhem - 07-18-2012
A little OT but the whole "old files" reminds me that Rick was going to post a picture/sketch of how he uses an old file as a chamfering tool in combination with a turning tool (if I remember the description correctly). So, whilst you have your pencil and paper out Rick
RE: mini mill - Rickabilly - 07-18-2012
(07-18-2012, 06:32 AM)Mayhem Wrote: A little OT but the whole "old files" reminds me that Rick was going to post a picture/sketch of how he uses an old file as a chamfering tool in combination with a turning tool (if I remember the description correctly). So, whilst you have your pencil and paper out Rick
The memory ain't what it used to be
I'm now trying to remember which champhering tool that was, was it the freehand one or the one I clamp into my toolpost.Best regards
Rick
RE: mini mill - Mayhem - 07-18-2012
One you clamped to your toolpost but why not show off both?
RE: mini mill - dallen - 07-20-2012
Rick
The two scrapers that I made all I did for sharpening them was to slightly round the end of the carbide and put some bevel onto the top with a bench grinder, then I have found that the straight one cuts better all across the edge if I hold it vertical and run a diamond hone straight across the edge at a 90 degree angle.
RE: mini mill - Rickabilly - 07-21-2012
I have drawn up an A4 page's worth of diagrams for the "right" way, although the right way is the way that works for you, I will try to get the scanner up and running today so that y'all can see how I was taught, suffice to say that the traditional scraper is double sided, that is when the first side losses it's edge you simply turn it over, so as you might have guessed no "bevel" but honing at 90 degrees does make sense.
Best Regards
Rick
PS while I was at it I drew up the dburring tool for Darren as well the photo was a no-go as I'm off my feet again :(
RE: mini mill - Rickabilly - 07-21-2012
Hello All,
Please see attached sketches, the first shows the process of converting an old file into a flat scraper.[attachment=2471]
The dimension "X" is the file/scraper lengthand while a bought scraper will have no teeth on the faces when I make one from a file I usually just dull the teeth off on a belt sander as the pattern actually makes it easier to control when oily.
The edges are necked in as can be seen in the second image on the scraper sketch as this allows scraping close to a stepped edge,
The front is radiused so that the corners never dig into the work piece,
The front 1/3rd of the tool is tapered to half of the original file thickness as this helps controlability, if the front edge is too thick it is difficult to see the scraping in progress,
Grinding the cutting edge is critical there is no "bevel" but the edge is hollow ground on a 4"-6" ally oxide wheel, I do it by eye nowadays but was taught to use a jig as drawn, the scraper should point directly at the axis of the wheel which will give an edge that is just less than 90 degrees on both sides of the scraper, and it is best to leave the grinding marks as these aid in starting a "Scrape",
To finish sharpening the tool, lap the top and bottom faces either on a stone or diamond lap, do not use wet and dry paper as this blunts the edge, some people hold the scraper at 90 degrees to the stone and polish the hollow ground edge, but I find that this reduces tool life and grooves the stone badly which ends up rounding the edges badly which means a blunt scraper.
The second attachment [attachment=2472] is the sketch of my deburring tool that I often fit on top of my turning tool in a lathe, as the top face of many tools is at centre height by putting this piece of file on top and upside down the cutting edge is automatically at centre height and can be used on the back side of a job without stopping and reversing the lathe, simply swing the toolpost around and you can deburr or add a champher to the bore or OD of most jobs,
1, standard file,
2, file with teeth removed, showing cut lines,
3, showing how it sits on a normal tipped tool,
4, same as 3,
5, how it is used,
As an apprentice we were trained to always fit a shim on top of indexble tipped tools to prevent scarring of what were then very expensive tools, most folks don't bother nowadays, this idea was a variation on a shim made from an old file and sharpened, when you get used to something like this it is really handy, if you've never tried it you'll never miss it, it is particularly handy in a single place tool post, not so much when using a four place post, or a quick change.
There is another version that clamps under the first and second clamping screws and while is upside down, so used on the back of the job but instead of hanging out the back this one sticks out from the side of the main tool so can be used without moving the toolpost orientation which is useful when you need to retain the calibration of the main tool but still want to deburr or champher a job with a tool in the lathe rather than as a post machining operation. This method limits how close you can work to chuck jaws or large shoulders.
One very important thing to remember when modifying files for use as cutting tools is to keep them cold during grinding processes, Many machinists do not realise just how fragile the hardness of a file is, with some grades of Carbon steel losing some of their hardness if the metal exceeds 120 degrees C, so that means if it goes Psst when quenching you've already ruined the hardness. Most folks think that a colour change is required, it isn't, if the colour does change it really is all over though.
Best regards
Rick
RE: mini mill - Mayhem - 07-21-2012
Thanks Rick.
RE: mini mill - dallen - 07-21-2012
Thanks Rick
I have tried to make scrappers before but was never really successful at doing it, I can see now that its mostly the way I was grinding them that didn't work. I have a bunch of files from when I was working in the plant that I can mess with now that I have some good instructions on how to do sharpen them
Rick whats your thoughts on using say d2 flat bar and hardening and tempering it for scrappers, and another question is would say a leaf out of car spring be hard enough to work.
DA
RE: mini mill - Rickabilly - 07-22-2012
Hello DA,
Car leaf spring, Hmmm, maybe but there are probably better things to use, leaf springs are all about resilience, not holding an edge, any good tool steel will work but I know that the professional ones are actually made out of file blanks so can't imagine a better material to use than an old file except maybe the carbide that you are already using, sharpened using a silicon carbide wheel to the same geometry that I have provided and you are likely to have a good usable relatively cheap tool that isn't as prone to wear as a carbon steel unit.
I made one out of a piece of HSS parting blade and it worked very well, and I used to make "three square" scrapers out of three fluted HSS taps, I suppose I'll be drawing up a three square scraper diagram now as well
, three square scrapers are the triangular file equivalent of the flat scraper, with three cutting edges running along the length of the tip of the tool in a triangular shape, used for deburring and scraping inside holes and other concave shapes.Best regards
Rick