Filingng jigs with centre pivot, and accounting for the curve to blade tip?..

F

FloWolF

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Sep 15, 2017
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Cutting the primary bevels on a few blades using a hastily lashed up ball joint based filing jig and I'm struggling to get the bevel right up to the tip...

The 2.5mm thick blades are to be stubby bushcraft ones, and will have around 3 1/2 inches of sharpened edge. The edge's 'belly' slopes gently along the length, then a fairly steep curve up to the tip - if I mark the cutting radius of the file on the clamping board, and set the majority of the edge on the same radius, the tip sits a good 1/2 inch further back and going for the same width of primary bevel surface as the rest of the blade (which leaves me about 0.5mm of un-sharp edge before HT time), the file crosses the midpoint completely leaving a finished edge with the bevel still a couple of mm short of where I want it.

Do I need to be re-clamping my blade with the curve and tip front and centre and file this part of the bevel separately to the main belly of the blade?

I've just used this jig to file and sand primary bevels on 12 single inside curved mushroom foraging blades, and 8 double inside curved (one on main body of blade, another short scalloped edge towards the tip) mushroom blades - it was tricky as the radius the jig cuts at is opposite the radius of the inside curve of the blades, but I made it work. I was expecting these little blades to be easier though, but so far I'm a little foxed...

Cheers for any helpful advice folks - I've already tried to search out the info but it's a bit like the needle and haystack scenario, only it's the needle I'm looking for amongst a load of very similar looking, but ultimately dissimilar needles. ',;~}~

Shaun.
 
Shaun,
I don't like jigs for filing bevels. Here's why - it can only file at one set angle. However, as you move toward the tip the angle will change because of the taper. This makes the tip come out wrong when using a jig.

It takes a few tries ( OK, maybe a few dozen tries) to get flat grinding down by hand, but your brain does all the fancy math and maks things come out right once you get some practice.
 
Hi Stacy, thanks for the reply - appreciated.

However can we just assume for the moment that I don't have the belt grinder option?

I'm aware these jigs don't hold consistent angles and fully realised this when I built a small honing jig some years ago based on the same idea, however with the honing jig I am free to re-position the blade constantly - just about every stroke if necessary as the forces are relatively small compared to filing, and all that's needed to support the blade are magnets and an adjustable backstop, so the issue is mostly negated...

However when I started this batch of 27 knives I had planned to use my tiny belt sander, but it's really not up to it, only a couple hundred or so Watt motor, and a very short belt that wears quick and doesn't flex at the edges - I'd have made a jig for this too for the 'straight' blades, but I have shaped and sharpened single blades on it freehand in the past when I had the time and my hand and eye were fully in - been mostly out of the workshop for too long for various reasons, and now am only getting a few hours/week to get this job done - not got the time or materials/consumables for the practice I need to get crisp bevels on that little Aldi special 'Powercraft' grinder/sander...

But I do know how to lash up these jigs and I have this one here, now, along with a brand new (on the flat side anyway) 10 inch (Nicholson) and a 12 inch (Simonds) second cut half round files plus loads of wet'n'dry I can fasten to the files to clean up the file marks afterwards - worked really well for the 20 various curved blades - just need to know how the folk that DO use these regularly, cope with the angle change issue when moving along the blade and then sweeping backwards towards the tip - anyone?..

Cheers!

Shaun/FloWolF
 
Have you watched Aaron Gough's filing jig video? He cover's most of the quirks about using one. I used to use one years ago, but it wasn't a fixed pivot, and you had to sort of 'twist' the file as you filed into the belly and tip. I remember a video I watched when I made it in which the guy used the term "Kentucky windage" (compensating for wind and gravity when shooting at a target at a distance) to describe the motion that the file makes, which I thought was about spot on.

Anyway, if you haven't yet, watch this vid and see if it helps.


~Paul
My Youtube Channel
... (It's been a few years since my last upload)
 
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Thanks Paul most helpful - no I hadn't seen that one yet, I'll watch that asap - dodgy ancient PC was playing up and consequently I hadn't watched any youtube video for ages, but you've reminded me that I have that issue fixed (for now) - I'll let ya know how I get on - I've got the 2nd one to file up later today.

Cheers again! ',;~}~

Shaun.
 
Stacy E. Apelt - Bladesmith said:
Shaun,
I don't like jigs for filing bevels. Here's why - it can only file at one set angle. However, as you move toward the tip the angle will change because of the taper. This makes the tip come out wrong when using a jig.

It takes a few tries ( OK, maybe a few dozen tries) to get flat grinding down by hand, but your brain does all the fancy math and maks things come out right once you get some practice.
Click to expand...
Stacy , we are talking about under one degree on four inch blade .Can free hand grinding achieve this ?
 
FloWolF said:
Cutting the primary bevels on a few blades using a hastily lashed up ball joint based filing jig and I'm struggling to get the bevel right up to the tip...

The 2.5mm thick blades are to be stubby bushcraft ones, and will have around 3 1/2 inches of sharpened edge. The edge's 'belly' slopes gently along the length, then a fairly steep curve up to the tip - if I mark the cutting radius of the file on the clamping board, and set the majority of the edge on the same radius, the tip sits a good 1/2 inch further back and going for the same width of primary bevel surface as the rest of the blade (which leaves me about 0.5mm of un-sharp edge before HT time), the file crosses the midpoint completely leaving a finished edge with the bevel still a couple of mm short of where I want it.

Do I need to be re-clamping my blade with the curve and tip front and centre and file this part of the bevel separately to the main belly of the blade?

I've just used this jig to file and sand primary bevels on 12 single inside curved mushroom foraging blades, and 8 double inside curved (one on main body of blade, another short scalloped edge towards the tip) mushroom blades - it was tricky as the radius the jig cuts at is opposite the radius of the inside curve of the blades, but I made it work. I was expecting these little blades to be easier though, but so far I'm a little foxed...

Cheers for any helpful advice folks - I've already tried to search out the info but it's a bit like the needle and haystack scenario, only it's the needle I'm looking for amongst a load of very similar looking, but ultimately dissimilar needles. ',;~}~

Shaun.
Click to expand...
Can you take picture of knife you try to grind on file jig ? I do that way many knives...............
 
Well I watched the vid thanks, and it did help me 'see' how the file was supposed to move (I got really in tune with things like this some years ago, but not keeping up with workshop stuff enough and then the birth of my little lad 22 months ago and what can I say - baby brain + out of practice), but my edge curves up towards the tip/spine much sharper and this makes the issue worse than with the blades in that and other similar videos.

I didn't get chance yesterday afternoon to start another, but I did get time to do do one side of a fresh blade after our little one had gone to bed last night and before the Mrs. put the telly on (because this is noisy work filing steel on a wooden jig clamped to a wooden dining table) for the home when the telly is on... in fact it's too noisy after an hour even if the telly is not on - the Mrs. liking it to having a large dog constantly barking in her ears heheheh...

The problem is of course, as soon as you move to the sharply rounded tip angle, the file must be held manually at a 'twist' angle to match how the jig holds it 'flat' for the rest of the blade - to help me with this I clamped a strip of 2.5mm scrap from the blade steel at ~90 deg. to the tip (running from tip towards rear of the jig), so even though this means I have more metal to remove, it helped stop the file twisting away from where it needed to be and I completed the first side reasonably successfully.

However for some reason this puts the belly of that curve at such an angle to the file pattern, that I found it almost impossible to stop it ploughing a strip of deep parallel furrows right there centre of the belly - changing the angle of sweep to the filing motion didn't help for some reason, so after doing the other side I may try finishing off the belly>tip section by moving the blade so the belly>tip section is front and centre on the jig and on the same file cutting radius as the bulk of the edge (so should be no need to blend 2 slightly diff. bevel angles), otherwise I'll be sanding these for hours extra afterwards.

Anyway cheers again, looks like it's coming under control, heh... ',;~}~


Shaun/FloWolF
 
Natlek said:
Can you take picture of knife you try to grind on file jig ? I do that way many knives...............
Click to expand...

Yes I can take photos no problem. Does this forum accept directly uploaded photos? Only I don't use any 3rd part hosting like photobucket etc.

Cheers Natlek,


Shaun.
 
So it appears I can't upload an here image without a paid subscription - will have to see if I can find somewhere to host them then post a link, perhaps...


Cheers!

Shaun/FloWolF
 
Well, that didn't go as well as I was hoping - first side done and it looked balanced right up to the tip, but doing the 2nd side it was obvious the grind was still over-steep at the belly>tip section. I've re-set up the jig now to do the front section separately, but held at the same radius as the main body of the blade will be, see how that goes! Meanwhile I've reground the blanks I'd worked on to give me fresh meat to go on so they will still be good blades just a tiny bit smaller that they were.

I'll link some more images when I get chance.

Shaun.
 
When you fix knife to jig make sure that edge is parallel , as you set it up You have even greater angle on belly and tip ....Also when you turn the other side you have to set up /must/ in the same position if you want equal grind on booth side .

4wM34Um.jpg


When you grind from ricasso to tip or tip to ricasso don t grind right up /by scratches looks that you grind right up ,that you in same time don t move file on side / grind , move the file in angle towards tip or towards ricasso ....
Sorry , my english is not that good to explain better , look the picture I think it s clear what I mind ?
8LpH5LK.jpg
 
Well, that didn't go as well as I was hoping - first side done and it looked balanced right up to the tip, but doing the 2nd side it was obvious the grind was still over-steep at the belly>tip section. I've re-set up the jig now to do the front section separately, but held at the same radius as the main body of the blade will be, see how that goes! Meanwhile I've reground the blanks I'd worked on to give me fresh meat to go on so they will still be good blades just a tiny bit smaller that they were.

I'll link some more images when I get chance.

Shaun.
Natlek said:
When you fix knife to jig make sure that edge is parallel , as you set it up You have even greater angle on belly and tip ....Also when you turn the other side you have to set up /must/ in the same position if you want equal grind on booth side .


When you grind from ricasso to tip or tip to ricasso don t grind right up /by scratches looks that you grind right up ,that you in same time don t move file on side / grind , move the file in angle towards tip or towards ricasso ....
Sorry , my english is not that good to explain better , look the picture I think it s clear what I mind ?
Click to expand...

Hi Natlek thanks again for the reply.

Regarding the blade being not parallel to the edge - I have it like that on purpose - with a single pivot point for the guide rod, the file has a cutting radius - a curved line at whitch it will cut at a single angle - I have the blade mounted aligned best as possible to one of these curved lines - if I had it straight/parallel with the front of the jig, the file would be cutting at a shallower and shallower angle the further along the blade from the centre of the jig you get. Do you see what I mean?..

And yes I have both positions for left and right sides of the blade matched it may not look it from the pictures and because the jig is only a quick temporary build from scrap wood and none of the angles for building it were measured, but the centre line is accurate and square-on, and I have lines marked for where the file cuts at different radiuses, then the blade is measured into place, the jig marked up and the screws inserted.

The gouges on the blade I mentioned in a previous post - I was in fact moving the file at an angle to the blade, but when it hit that radius at the belly it pulled the blade into a diagonal/angled slide that was perfectly in line with the criss-cross 'X' pattern of the file teeth, and that's how those plough marks came about! I tried very hard subsequently to not let it happen, but the only way for me was to take softer strokes at that point.

Thanks again for taking the time to offer help, cheers!

',;~}~

Shaun/FloWolF
 
FloWolF said:
Well, that didn't go as well as I was hoping - first side done and it looked balanced right up to the tip, but doing the 2nd side it was obvious the grind was still over-steep at the belly>tip section. I've re-set up the jig now to do the front section separately, but held at the same radius as the main body of the blade will be, see how that goes! Meanwhile I've reground the blanks I'd worked on to give me fresh meat to go on so they will still be good blades just a tiny bit smaller that they were.

I'll link some more images when I get chance.

Shaun.
Click to expand...
Look , it is 2.5mm thick steel and very shallow grind .With good file it will take less then 10 minutes time to grind both side . Fact that you can t grind right say that somewhere you make mistake ...... Now I see on your picture that steel bar that hold file don t go full length ......that can be reason for your problem , too. I think that way you cant keep constant angle when you work , it must flex when you apply pressure................and that constantly change grinding angle .............Did you have center line on edge ? It help to see how and where you need to file ?
 
Heheh, oh I'm definitely making mistakes! To be honest I think my filing technique is uhhhmmmm... rather poor to start with - it never was that good even when I was in-practice.

Ideally I could do with having used 8mm rod and pivot/ball joint, and as you say, should have the bar running the full length of the file to stiffen things up properly, but the metal rods and pivots are what I got from the honing jig I made some years ago (acrylic blocks with diff. grade diamond plates attached that then slot onto the 6mm rods etc.) and they are perfect for that job but are too short to run further along the file.

I did manage to file-grind workable bevels on a total of 20 inside curved blades from the same steel, using this jig with those rods attached to the (half round) files the same way though, and while it took time and was a struggle, it worked in the end - I think the rods/attachment may be aggravating the issue but I don't think they are as much to blame as I am, with my poor technique and with me being rather 'off my game' these days - I need to regain more focus/presence of mind so I can see and sense better what is happening with every file stroke - I maybe just need to wake up more and remember what it means to become one with the tools and the work, in the moment, and that's down to me isn't it!

Oh and yes I have a centre line marked on each - I used a small strip of off-cut from the blade steel, sharpened it to a point slightly off centre, stove-top hardened the tip then used it and a thick piece of flat glass to mark the blade edges, from one side up first then the other next to give 2 parallel lines centre of the blade edge to grind up to.

I shall persevere for now and see how I get on. Thanks again for taking the time to offer help, I truly appreciate it.

Cheers Natlek, and be well,

Shaun.

Just to add - using the filing jig for this little bunch of blades (including the 20 already beveled) was my 'Plan C!' That's why it's all a bit hasty and me more poorly prepared even than usual - I was supposed to be using the little belt grinder I have but it just wouldn't do what was needed for the curved blades, and neither would the zirconium spiraband wheels (Plan B), least not in my hands so I resorted to filing instead, and uhhmmm haven't looked back! Heheheh... ',;~}~
 
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Good evening good folks,

Well I took a shot at mounting the blade in different positions for the main section, and then the belly>tip trying to keep the 'edge' on the same filing radius each time, and it worked, after a fashion - there is a tiny 'just' visible transition right about where you'd expect one were one to arise, but nothing that won't get levelled out as I progress towards polished (or whatever finish I settle on)... and as I worked, thinking on what's been said here and on the videos I watched and finally started to 'wake up' and 'see' more of what was going on...

... and I had some thoughts - please anyone feel free to re-steer me if I've gone off track with them (below)...

I finally started to realise (my dubious skill levels notwithstanding) the limits of that roughly assembled scrap-softwood jig, and I started to realise also why these blades were giving me kinds of bother on it, that the 20 curved 'mushroom' knives hadn't, and it was just down to the bevel angle - the shallower angle of the primary bevel (small secondary bevel to be added after HT) on the mushroom knives reduced the effects of the file angle changing slightly, whereas the steeper 'scandi' single bevel exaggerated any angle differences.

I also realised that in my present state of unpractice/'newby-ness'/anxiety I was overthinking at least some aspects, and went back to wondering why others using similar jigs were not having the issues I was having, despite not fussing over mounting the blade along the actual file cutting radii, and then I noticed how much further away from the work-piece they all had their guide rod pivots, whereas I had just the bare minimum to account for a full file stroke - the further away pivot makes a much wider/gentler radius which again reduces the filing angle differences working along the blade length.

So cutting to the chase to stop making a long story longer - I got myself some nice, well seasoned, flat oak board, then cut out and assembled a much tighter, more solid and fully squared-up jig, with longer foot to it to accommodate the longer and thicker 8mm x 800mm steel guide rod and new ball joint I have coming. Meranwhile however I have put the old, short 6mm rod/pivot on there so I can keep plucking away at these blades if I feel I need to get on with them, and then I marked the work holder up with a set of crisp(-ish!) cutting radii lines at ~1cm spacings, see how I get on.

If these blades were all for me I'd have taken them freehand to that tiny belt grinder and worked it all out as I went on, but they aren't all for me and this makes me nervous...

Anyway thanks again folks for your patience and indulgence - I suspect I can be a bit of a PITA to deal with sometimes - cheers!

Shaun

(2nd attempt - wrote all this out last night but the PC ate it!)
 
Thought I'd post a few pics of how I got on in the end, after rebuilding the filing jig with flat oak boards and a longer 8mm guide rod, last picture - the other curved (mushroom foraging knife) blade's bevels were ground in on the jig made of old pine floorboard and a short 6mm guide rod.

Anyhow here's a few of the curved knives made up, and the first off of the 5 bushcraft/woodsman. Cheers for the tips and advice folks.


https://imgur.com/unkJroO

https://imgur.com/xGNXVzZ

https://imgur.com/xGNXVzZ

https://imgur.com/5POoF0U

https://imgur.com/veC1MSE

https://imgur.com/ynMTTH5

https://imgur.com/mwWsxLp

https://imgur.com/AHN408A


Shaun/FloWolF
 
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