Thread: Sharpening Rasps. Is it possible?

At the foot of this thread there are links to associated topics. I did look up some of them, but many of the links were either missing or did not relate to the posts. However, the thread by DSEL did mention that he used battery acid (sulphuric ?), although not for long periods being significantly more aggressive than my solutions which have very mild acidity.

Another acidic possibility has just occurred: Cola, which I think could have a PH of around 3.5.

Regards
Paul

Originally Posted by Bushmiller

At the foot of this thread there are links to associated topics. I did look up some of them, but many of the links were either missing or did not relate to the posts. However, the thread by DSEL did mention that he used battery acid (sulphuric ?), although not for long periods being significantly more aggressive than my solutions which have very mild acidity.

Another acidic possibility has just occurred: Cola, which I think could have a PH of around 3.5.

Regards
Paul

I’m sorry Paul, but with my pleasant am fine dissipation, an high moral grounds, if this this thread gets any more acidic, I will have know course but too find a more suitable pleasurable thread too follow.

Matt[emoji849]

Paul

As I was already setup to try out the rag wheel treatment, I did a brief test run with a small worn rasp and got a result, which I would be happy to report on here or if you prefer in a separate thread.

What would be your preference?

Originally Posted by GraemeCook

Or the cruder version ... : "You cannot polish a faeces" ... unless you are Martin.

My mate Martin the eccentric scientist has a coprolite - litterally a fossilised dinosaur faeces- only from a small dinosaur - which he has polished to a deep sheen. It looks like semi-opaque amber, quite nice, and few realise the source, although the shape is a giveaway.

[Explanation: Faeces is a word which, in these political correct times, is acceptable to Big Brother the auto-editor, rather than that subversively common terd. I kid you not.]

I literally was going to make the same joke, but I didn't know someone actually polished a fossilized .

Why make the joke? In varnishes, (semi)fossilized resins are actually a little harder and can generally make varnish that can be polished. Softer varnishes are durable but not hard enough to take a polish.

Originally Posted by NeilS

Paul

As I was already setup to try out the rag wheel treatment, I did a brief test run with a small worn rasp and got a result, which I would be happy to report on here or if you prefer in a separate thread.

What would be your preference?

Neil

I would be comfortable with either, so whatever suits you.

Regards
Paul

Originally Posted by NeilS

Paul

As I was already setup to try out the rag wheel treatment, I did a brief test run with a small worn rasp and got a result....

I picked two 8" rasps for the test run, the one on the left was well past its useable sharpness on the round side and the one on the right, which is hand stitched and almost unused, as the control...

Test rasps.jpg

I ran the back of the teeth on the blunt file over the rag wheel loaded with cutting compound, rasp teeth facing away from wheel rotation. One pass over the full length and a second pass over just the tip half end...

After rag wheel.jpg

That left a bright area on the back of the tips and a build up of buffing compound in between the teeth. I removed the compound by dipping it in metho and swiping across with a wire brush, which was quicker than I anticipated.

I used a piece of old hard redgum floor joist as the test piece and ten strokes with the rasp for each test run, then measured cut length back from edge...

20230501_164155.jpg

1. Cut with the unused control rasp - 22mm
2. Cut with the worn rasp before rag wheel - 17mm
3. Cut with worn rasp after rag wheel - 19mm
4. Cut with worn rasp using just the tip half end - 20mm

So, there was a measurable improvement in the cut from the worn rasp after the rag wheel treatment. A double strop on the tip half end (ie two passes over the rag wheel) showed some additional benefit.

I then attempted to test how durable the 'refreshed' teeth edges were by using it on the same redgum until it was back to cutting as poorly as it was before rag wheeling...

20230501_164354.jpg

That gave 28 x 10 strokes + the initial 2 x ten strokes = 300 strokes before the the rasp was back to cutting only 17mm with every 10 strokes.

Other than saying that stropping on the rag wheel is very quick, I have no idea how useful this method is compared to any other or whether an extra 300 better cutting strokes from using this method is worth the effort.

The other unknown is how many times this method could be repeated on the same rasp and still get worthwhile results. From my experience with turning tools and what the farriers are saying there would be diminishing benefits with repeat stroppings.

Neil

That is most interesting and thank you for taking the time to conduct the test. I did note that in the other thread I linked to from DSEL, he mentioned three "re-sharpenings" were the limit of usefulness with his technique (soaking in battery acid).

I have some buffing wheels, which are the stitched type. Will that work for David's "unicorn" technique? If so, what colour compound is recommended? I think I have grey, white and green: maybe some black too.

Even if my testing with vinegar and citric does not produce any sharpness benefit, it certainly removes the crud that a wire brush fails to dislodge and this could make for a better sample to try something else as far as used rasps are concerned.

Regards
Paul

Originally Posted by Bushmiller

I probably should have described it as a farrier's rasp, but horse and coarse rhymed better!

Of course, a course, horse farrier's rasp.

Originally Posted by Bushmiller

I have some buffing wheels, which are the stitched type. Will that work for David's "unicorn" technique? If so, what colour compound is recommended? I think I have grey, white and green: maybe some black too.

Paul

Before answering those questions on the buffing method, you might like to read the following first.

Thinking about the rag wheel buffing method, that makes sense for farriers as they usually have a buffing wheel on hand for refreshing an edge on their hoof knives, etc.

That got me thinking about what I have on hand for sharpening things; I'm always sharpening something! Lately I have been using 50mm diamond cut off wheels in a Dremel for sharpening my large crosscut saws.

uxcell 10 Pcs 50mm Diamond Coated Cut Off Grinding Wheel Discs w 1/8" Mandrel : Amazon.com.au

Why not try one of those diamond wheels on the rasp? Nothing to lose as that blunt old rasp is long past its best.

So, I took to it with two approaches.

I had a rough old go at grinding the face of the teeth on half of the rasp nearest the tang until most of the bright spot had gone from the top of the teeth in each row. Without looking at the result under magnification I expect the teeth heights were left all over the place and who knows what I did to the rake angle!

On the tip end of the rasp I had a go at grinding off some of the top back of the teeth. As you will see from the following photo, this was an extremely rough job as the grinding wheel covered up what I was attempting to grind...

Rasp after diamond cut off wheel hack.jpg

Despite the dog's breakfast that I made of the teeth, the rasp began to cut quite well. There wasn't much difference between the front and back of teeth grind in terms of wood removed, although the cut coming off the section with the grind on the front of the teeth did feel smoother. That may have just been that less rake was better suited to the hard wood test piece.

Next I tested for depth of cut and durability. Prior to the buffing wheel treatment the old rasp could only cut back 17mm, which improved to about 20mm after buffing, but was back to 17mm after 300 strokes.

After the diamond wheel hack, the rasp could cut back a length of up to 23mm with ten strokes. The new stitched control rasp did up to 25mm on the same section seasoned redgum.

Cut length after diamond cut off wheel hack.jpg

I then went on to see how long the old rasp would cut with the diamond wheel 're-habbed' teeth...

20230502_103414.jpg 20230502_103631.jpg

It kept cutting well to the feel for 75 x 10 strokes = 750 strokes, but by measurement it was only cutting back 20mm by then, which was as good as it managed in my previous experiment immediately after rag wheel stropping.

At a guess it took me about 8 minutes to do the diamond wheel hack on the teeth, but I was using a tool that I'm familiar with, but looking closely at the top photo in this post I'm sure anyone could manage better if they took the time.

Several thoughts, the more irregular positioned teeth on a hand stitched rasp would be more difficult to do with this method, but larger raps would probably be easier than this little one.

I'll try to get some close up photos of the carnage that I managed with the diamond wheel.

Originally Posted by Bushmiller

I have some buffing wheels, which are the stitched type. Will that work for David's "unicorn" technique? If so, what colour compound is recommended? I think I have grey, white and green: maybe some black too.

Yes, Paul, I use an 8" stitched wheel on the bench grinder with the outer row of stitches removed to make it slightly more flexible at the rim. On my turning tools I use the green chromium oxide compound where I'm looking for a very fine edge, but for the stropping on the rasp teeth I used brown and would have used black if I had it.

Here are the before and after photos of the rasp teeth, the second one is after my assault on it with the diamond wheel (the light coloured areas)...

Old rasp before I attacked it.jpg

Close up of teeth after diamond wheel.jpg

Hard to believe that it cut better like that after the diamond wheel assault, but it did.

If you have a rasp that is past being usable, or it never was, no harm in giving it a go. You can hardly do a worse job than me and you might rescue it to use a bit longer or get a user out of it after all.

It may not look pretty, but with the cost of rasps and files the way they are now who cares about how it looks as long as it works.

Going on my experience with this, my preference would be to use the diamond cut off wheel rather than repeated brush ups on the rag wheel.

Neil

Thank you for all your efforts. You have given me and, I suspect, anybody who ha glanced at this thread plenty to ponder. I will have a look at those diamond wheels. I only have the fibre mini cut off discs for the dremel style tools.

Something that springs to mind following your endeavours is to freshen the face with a cutting/diamond mini wheel and use the buffing method on the backs. I do think your method would be exceeding difficult and/or tedious on finer grains, but clearly doable on the coarse versions.

Regards
Paul

Thought some might find this an interesting read,

Hand making files.


Also I wonder if a rasp could be be “Repaired” sharpened by re punching it ?.

http://www.hawleytoolcollection.com/...0-%20Files.pdf


Cheers Matt

Originally Posted by Simplicity

Paul,


How to cut Make Organic shapes. - YouTube
[emoji849]

Thanks Matt

The 4-In-One is featured at 13:30mins.

Regards
Paul