How to calculate honing guide protrusion?

[Wrongfoot]

I've a nice little honing guide, nothing vintage or special, but it works.
It has protrusions marked on the side for different angles - 50mm for a 25 deg angle and 38mm for 30 deg for plane irons mounted on the top, 40mm for 25 and 30mm for 30 for chisels mounted lower. I don't use it a lot as I mostly freehand my plane irons and chisels.

However I've a few of the Record 405 cutters to dress back to 35 degrees and as there's rust damage to the faces, I'll have to take off a bit... The tungsten steel on those is hard stuff as this'll take a while I'll get tired free handing and no doubt round the iron a bit. I'd prefer not to so I want to dress them back using a guide on a course diamond stone bought for the purpose. Unfortunately those irons need a 35 degree angle... How do I calculate the protrusion for a 35 degree angle?

I can trial it with an angle finder and I may have to do so, but I wondered if anyone knew how to go about the maths for this?

 

[Wrongfoot]

It's a guide identical to this one https://hardwickandsons.com/products/honing-guide if that helps anyone who has a similar guide tell me what protrusion they use for angles other than 25 and 30?

 

[Ttrees]

Can you not get a blank of timber and draw the angle on the edge, line it up with the cutter in the guide, flip it around and butt it against whatever blank you use for guide setup, mark a line at the edge of the cutter for quicker setup?

Sorry, not what you might want to hear but I will say it anyway, since there's no mention of this
anywhere that I have read/seen....
Use the corner or high spot on the stone to eliminate the camber on the iron.
Another reason why diamond hones are brilliant, because working the corner is so much faster and surer than working on a high spot on each side of the stone.
reading the above, I don't mean flipping the stone on edge, but that might be even better if it were slim.
I have nothing to dislike about a narrower stone and never heard an argument for a wider one, so should not present any problems in future.
WIlling to be corrected on this, but I have yet to want for a wider stone.

I use a cheapo 2 quid 400grit DMD plate for this nearly every day to eliminate the camber for
using the close set cap iron, as I'm still finding it difficult to do in a few seconds,
and it normally takes me some fiddling to get the perfect camber that's required for it to work.
I might spring for an Ultex hone yet, and use the heck out of those corners.
Tom

 

[ED65]

You can just match the angle of the existing bevel, but the key thing for speed and repeatability is only having to do it once. So simply glue a stop block to a scrap of wood so you can set the same projection again in a trice.

Stop blocks are much faster than setting angle by measuring projection. While you're at it you might want to glue another beside it for 25° for re-establishing the primary on normal tools more quickly if that's something you do manually on a semi-regular basis.

 

[Trainee neophyte]

You could resort to your school geometry, using a right-angle triangle and Pythagoras.

Or get the internet to do it for you: https://www.calculator.net/triangle-calculator.html

 

[samhay]

>You could resort to your school geometry, using a right-angle triangle and Pythagoras

I started writing a reply in this vain.
It requires some initial quite accurate and awkward measuring (for the opposite length) and then a scientific calculator (or web app) for the tan-1 calculation.
I expect for most of us it will almost always be preferable to mark out the angle and measure, then note this down somewhere for next time.

 

[xy mosian]

Calculations will be tricky. As the angle of the guide's table changes, the height of the front edge to whatever is used for sharpening, stone or otherwise will also change.
I would suggest setting a sliding bevel to 35 degrees. Place your blade in the guide clamp loosely. Insert the blade end into the mouth formed by the bevel stock and blade. Adjust the position of the guide, on the blade, until that blade falls neatly onto the blade of the bevel with the guide's wheel on the stock. Meaure the distance of the leading edge of the guide to the point of the bevel included angle, either directly or by marking the bevel blade with a pencil or some such.
That should give the answer to you question.

HTH. xy

 

[woodbloke66]

You can just match the angle of the existing bevel, but the key thing for speed and repeatability is only having to do it once. So simply glue a stop block to a scrap of wood so you can set the same projection again in a trice.

Stop blocks are much faster than setting angle by measuring projection. While you're at it you might want to glue another beside it for 25° for re-establishing the primary on normal tools more quickly if that's something you do manually on a semi-regular basis.

This is unquestionably the easiest way and is exactly how the Veritas Mk2 honing guide works - Rob

 

[ED65]

These setting boards can be quite small, the one I think I first saw was posted on Lumberjocks and was just a small piece of ply with a stop off-centre in the middle, for the two usual angles for primary/secondary. Here's a more comprehensive one which I think first appeared in a Fine Woodworking article some years back:

Here's another wrinkle on the idea, https://cdn.thetoolworks.com.au/wp-cont ... -100-1.jpg

 

[transatlantic]

Don't forget that the thickness of the blade plays a part too (depending on how you measure the projection)

So 25deg on a thin blade will have a different projection to 25deg on a thick blade.

Using the same projection for all your blades (irregardless of thickness) isn't a problem though, they'll just be 25 .... ish. But it does mean that some blades will need more material removed before you're at the cutting edge.

This is particulary a problem with japanese blades. I use a jig to sharpen mine, and the thickness from plane to plane varies so widely, that I have a different measurement projection per blade to achieve the same angle (and yes, I do realise that using a jig on japanese blades is a sin, but hey ho!)

 

[D_W]

If you're using an eclipse type guide, make yourself three blocks like this:
https://i.imgur.com/gCfSSAh.jpg

Or two, whatever you do (no need for three if you use a powered grinder). These are old and little used, but they served their purpose when I was learning.

You can put a blade in an eclipse style guide partially tightened, hone one bevel and then stub the guide and blade into the slightly steeper angle block and push it to the next higher angle.

If you like to sharpen narrow chisels in guides, the blocks can be narrower. Your angle will always be the same regardless of the thickness of the iron or chisel.

These are just CA glued onto a piece of scrap and I used them for years when I did use them and nothing ever came apart.

I've used a power grinder for a long time, so the first angle from this set never really got used.

 

[Wrongfoot]

Hey thanks guys.
I will almost certainly use an adjustable mitre gauge and reference to get going, thanks for the suggestions to keep a sane approach.

I was also interested in the math (just for the sake of geeking out) and had realised that as my honing guide references the underside (face) face for chisels all these will come out at an identical blade angle but plane irons sit on the top of the guide and so the blade angle will vary with blade thickness. If any posters want to post some trigonometry I'd still be interested. I tried to do the math using the known angles and protrusions marked on the guide but was obviously getting it wrong with results way off the reality .

My old cheap Stanley honing guide would be better for always getting a consistent blade angle (shame I've lost a round nut for it) but my Eclipse type honing guide I linked to above is better for making sure I grind exactly square. A square cutting face is v important on a 405, I don't think it matters as much on an adjustable Bailey type plane.

 

[RAF]

Stolen from somewhere:

So for plane irons, nail a block that is 1-1/2” from the edge of your 1×4. Label it 30°. Nail a block at 1-9/32” from the edge and label it 35°. Then nail a block that is 3-3/8” from one end of the block. That will be used to set your plane iron to sharpen a 15° back bevel on a plane iron.

Sharpen chisel honing guide

(Note: If you don’t know about back bevels, keep your pants on. I’ll do a blog entry on that later this week.)

Turn the block over.

The other face of the 1×4 is for chisels, which are held in a different notch in the honing guide. If you need to check the angles produced by your particular guide, clamp a ruler in the guide and use that to check the angle on a protractor.

If you have the ubiquitous (Megan taught me that word) honing guide, nail a block at 1-3/16” from the edge for 30°. Nail a block at 15/16” to get 35°. If you want other angles (I don’t), then you can figures those measurements out with ease.

 

[ED65]

Then nail a block that is 3-3/8” from one end of the block. That will be used to set your plane iron to sharpen a 15° back bevel on a plane iron.

Danger, danger Will Robinson!

 

[Jacob]

Have you thought of using one of these? It's called a "protractor" and gives you all the angles from 0 to 180º. They only cost £1 or so.

What you'd do is set the guide to match the protractor angle visually - hold it against the side and squint across. You could always measure and or mark it to avoid having to do it again. 35º is arbitrary anyway, a few degrees less would be fine , but perhaps not more.

 

[ED65]

If the existing bevels are satisfactory they are all that's required to set projection, and thence to make stop blocks for quick repeatability.

 

[Chris Knight]

The Rolls Royce way. Plan for a lie Nielsen version https://d3h1zj156zzd4j.cloudfront.net/p ... g-2019.pdf

Note that this immediately downloads the pdf - no intermediate page.

If you are desirous of being absolutely spot on, use a digital angle measure on the blade. It's extremely quick and easy and the digital thingy is also excellent for setting tablesaw blades, drill press tables etc. to the correct angle.

 

[Jacob]

The Rolls Royce way. Plan for a lie Nielsen version https://d3h1zj156zzd4j.cloudfront.net/p ... g-2019.pdf

Note that this immediately downloads the pdf - no intermediate page.

If you are desirous of being absolutely spot on, use a digital angle measure on the blade. It's extremely quick and easy and the digital thingy is also excellent for setting tablesaw blades, drill press tables etc. to the correct angle.

Pleased to see they mention a protractor :shock: but they spoil it somewhat with the complicated jig needed to use it :roll: . You just need to put the protractor up against the side of the jig/blade and read it straight off - easier than using a jig.
It's a classic case of how they make something simple look difficult and then sell you a gadget to make it easier, which actually makes it more difficult.

 

[D_W]

The Rolls Royce way. Plan for a lie Nielsen version https://d3h1zj156zzd4j.cloudfront.net/p ... g-2019.pdf

Note that this immediately downloads the pdf - no intermediate page.

If you are desirous of being absolutely spot on, use a digital angle measure on the blade. It's extremely quick and easy and the digital thingy is also excellent for setting tablesaw blades, drill press tables etc. to the correct angle.

Pleased to see they mention a protractor :shock: but they spoil it somewhat with the complicated jig needed to use it :roll: . You just need to put the protractor up against the side of the jig/blade and read it straight off - easier than using a jig.
It's a classic case of how they make something simple look difficult and then sell you a gadget to make it easier, which actually makes it more difficult.

I found that kind of thing invaluable at the very outset woodworking. Nobody brand new understands subtlety yet and what matters and what doesn't, so the paint by number effort is good. Use of a lot of edge tools for many hours will send you looking to rely on what you walk to the sharpening bench with, but I can't deny that I couldn't post pictures of my methods and expect a brand new person to get a good edge with a very high percentage chance.

 

[Jacob]

Just revisiting the LN page

Good that they admitted to the existence of protractors for the task, but true to the principle of "never give a sucker an even break" they have specified completely the wrong tool for the job! :lol:
It's so wrong that you can only use it with difficulty; upside down from under the table! A 50p plastic one from Smiths would do it much better.
Surely a coincidence but LN sell these expensive Starrett protractors themselves? :roll: $90
Oddly they also sell a protractor without a locking arm, which appears to be completely useless.
Being steel makes it worse. Transparent plastic is the way to go, but there's no money in it.
Mind you if you like doing things with the wrong tool, upside down, from under the table, LN are the people to go to.
Happy Christmas all. :ho2