# Simple Filing Guide for Lathe



## romartin (Jul 4, 2012)

This post describes a tool "Simple File Guide" which I built a few years ago and which may interest folks who, like me, have a lathe but don't have a milling machine. It supports the use of common or garden files under muscle power to make flats on round sections or cylindrical segments on flat sections with significantly better precision than can readily be achieved otherwise. In conjunction with a dividing head or a simple indexer based on use of the lathe gear train, the File Guide can help you to make good looking and sufficiently accurate polygon sections e.g. square or hex or matched flats on opposite sides of a shaft. 

The process makes use of the lathe, without power, to position and hold the work piece while the File Guide limits the motion of the file to ensure that only the desired excess metal gets removed. Depending on the application, the File Guide may be held in the Tool Post and the work piece in the chuck or the File Guide may be held in the chuck and the work piece in a machine vice mounted on the carriage.

The picture below shows the tool. 





A one page drawing is in the Download Section with the name "Simple File Guide.pdf". The handle is round to facilitate mounting in the chuck or the tool post. The two parallel rollers are made in PVC; they are what guide the files and need to be substituted when excessively consumed. The other parts are in mild steel.

The following pictures illustrate using the tool to give a hexagon section to the end of a rod. 




First the File Guide gets mounted in the lathe Tool Post with the plane of the rollers at a convenient angle so that movement of the cross slide adjusts the distance of the file surface from the lathe's line of centers. This adjustment is made simply by mounting a rod of the desired radius in the chuck and then moving the cross slide until the lower surface of the file is tangent to the upper surface of the rod. Lock the cross slide to maintain this position.





Second, the lathe gear train is set up to serve as an indexing tool for the angular position of the chuck. I set up the gear train to give a speed multiplication factor of 4. At the end of the train is a gear with 60 teeth so I end up with 240 index positions which supports all the numbers of faces I've needed and many others (2,3,4,5,6,8,10,12,15,16,20 ...). I fix the angular position of the chuck by inserting between the teeth of this wheel a fixed aluminium wedge firmly held in a block of wood. Naturally, as with the graduated wheels on the lathe slides, it is important to eliminate the systematic slack error by always turning the chuck, and hence the gear train, in the same direction.





Third mount the prepared work piece rod in the chuck. Note that to obtain distance "d" across opposite flats, it is quickest to reduce the diameter of the corresponding section of the rod to be 1.16 x d. 





Fourth position the chuck angle for the first face, block the chuck angle and file away until the file is turning both rollers of the File Guide. Repeat for the other faces.









The following pictures illustrate use of the File Guide to round the corner of a bit of scrap brass plate to be concentric with a bolt hole near the corner. The plate is mounted in the chuck by means of a mandrel through the corresponding bolt hole. 

First the File Guide is set up in the Tool Post as described above. 





Once the File Guide is set up, the mandrel is mounted in the chuck and the manual filing operation can begin gradually turning the chuck by hand through the angle needed to generate the circular section for the corner. In the example shown the angle is 90 degrees. The final strokes of the file should be light and you should see both rollers turning indicating that you have reached the desired radius. 





The following picture shows some other work products which have flats and/or rounds made with this tool, including the hex sections on all those 2mm nuts and bolts.


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## ProdEng (Jul 4, 2012)

That's a very useful but simple setup. I have seen some very complicated filing rests and been put off making one for that reason, same goes for indexing. The file is an underrated tool in the CNC age.

Jan


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## Noitoen (Jul 4, 2012)

A little refinement would be a little collar on the left of the rollers to make a precise stop to file those "spanner" recesses.


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## steamer (Jul 4, 2012)

Hello romartin,

I have a very similar set up I use a lot! For small parts, I find it's actually faster than setting up a dividing head, and I get more accurate results because the part never comes out of the chuck.

Dave


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## romartin (Jul 4, 2012)

Thank you for your replies.
Yes indeed Noitoen, the tool needs the collar you suggest. I'll replace those two end washers with ones with a larger diameter. Thank you for the suggestion.
And yes Dave and Jan, there is a certain pleasure in getting a satisfactory result through the coordinated application of both brain and muscle power!


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## Chriske (Jul 4, 2012)

Very Nifty...!

 Thm:


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## Ogaryd (Jul 4, 2012)

Hi Romartin,

    Thats a really neat useful tool. I'll have to make one soon.

                                          Thanks Gary,


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## Rayanth (Jul 5, 2012)

quite brilliant, I will have to add this to my projects list - thinking it will be a while yet before i can get a mill...

- Ryan


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## romartin (Jul 5, 2012)

Here is a photo of the revised tool with the larger roller stops as suggested by Noitoen. 
My original post said that I had put a drawing in the Download section but I discovered this morning that it wasn't there. I have now uploaded the drawing (one A4 page) and checked that it is there (SimpleFileGuide.pdf). It shows this revised version of the File Guide with the larger roller stops.

If anyone actually builds a tool based on this design I would be pleased to hear how it goes...

Ciao


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## Runner (Jul 6, 2012)

Hi Ian,

I must be thick couldn't find your pdf file, assumed it was in the plans section. Did a search on "SimpleFileGuide.pdf" and all I got was your last post. Maybe I need it stuck under my nose.

Brian


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## Rayanth (Jul 7, 2012)

http://www.homemodelenginemachinist.com/index.php?action=tpmod;dl=item404

It's the most recent file, if you click on "Downloads and Uploads" in the menu, but above shoul dbe a direct link.

- Ryan


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## Runner (Jul 7, 2012)

Thanks Ryan,

all the time I have visited this site I have never noticed the Menu on the LHS "Downloads and Uploads" etc. 

Brian


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## modeng2000 (Jul 7, 2012)

Thanks for posting your filing guide. I have made one today much like yours, adapting where necessary to suit the scrap box contents. I wish I'd had one before as it seems so easy to use.

John


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## Paolo (Jul 13, 2012)

Hello Ian....
nice idea and well done...
Best regards


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