Back Flattening

[woodbloke]

Further to the recent thread on flattening plane backs and Alf's excellent demo at the MiniBash last Saturday, I decided to have a go at Alf's method. She used a piece of 10mm acrylic plastic onto which was smeared a small quantity of 45g diamond paste, mixed with a little paraffin to form slurry. The idea is that the slurry embeds itself to a certain extent into the much softer surface of the acrylic and doesn't 'ooze' out the sides, as it may do with much harder float glass, and also doesn't break down.

I tried a slightly different tack in that I screwed a piece of 6mm acrylic to a bit of 15mm mdf and then bearing cut off the waste with the router. I then used coarse Silicon Carbide valve grinding paste (which is very fast cutting, much faster I think than the diamond that Alf was using.) After a few minutes pressure tho' this then breaks down into a much finer slurry and gives a smoother finish. I then wiped the old coarse slurry off the surface and replaced it with some fine valve grinding paste and repeated the process. After about 10 minutes total with the valve grinding paste it was onto the coarse DMT for a couple of mins to finish off.
This first pic shows one side of a blade with the tempering colours done by Newt a few weeks ago:

-

The shot above shows the polished back after about 12 minutes or so, it's certainly good enough to start grinding the primary bevel on the other side and then the 'ruler trick' to finish off. I'm not sure that the coarse paste wasn't a little too brutal to start with, but it's an interesting way to do the backs and very quick - Rob

 

[Paul Chapman]

That looks good, Rob. Some quite useful things are coming out of these get-togethers. And I bet people thought they were just about gloating :roll: :lol:

Cheers :wink:

Paul

 

[woodbloke]

Paul Chapman wrote:

And I bet people thought they were just about gloating

You're spot on there Paul, the primary objective of the MiniBash was the useful exchange of sawdusty info...the mere chance that so much gloatworthy metalwork just 'happened' to find itself onto my take off table on the day is nowt but a truly remarkable and unashamed coincidence :^o \/ - Rob

 

[JesseM]

Do you use side to side motion or circular motions on the acrylic? The reason I ask is cause from experience the side to side is much more destructive and was wondering what it would do to the acrylic in this case. The circular motion seems to cause even wear and I would think it wouldn't do too much.

 

[Philly]

Rob
I think it was 45 micron diamond paste - glad the valve grinding paste worked out. Need to give this a try myself.
A word of warning - don't try to flatten the backs on a tormek or a belt sander. It just doesn't work - you just make even more work for yourself. DAMHIK :roll: :lol:
Cheers
Philly

 

[JesseM]

Rob
A word of warning - don't try to flatten the backs on a tormek or a belt sander. It just doesn't work - you just make even more work for yourself. DAMHIK :roll: :lol:
Cheers
Philly

You can also add the Powered Veritas MkII to that list. I need to have some sort of electric shocker to stop myself from even trying. I always think this time will be different, but it never is.

 

[woodbloke]

Rob
I think it was 45 micron diamond paste - glad the valve grinding paste worked out. Need to give this a try myself.
A word of warning - don't try to flatten the backs on a tormek or a belt sander. It just doesn't work - you just make even more work for yourself. DAMHIK :roll: :lol:
Cheers
Philly

Phill - new it was 45 somat I've tried the side of a grinder and you're right....allot more work for yourself - Rob

 

[engineer one]

wot am i doing wrong then, mine seem ok?????

paul :wink: currently proving that his sharpening skills are enough to plane a couple of lumps of lime flat and straight, plus the legs and parts of the rear panels with my no 6, 41/2 and the ln62.

 

[Anonymous]

Rob

Any chance of a better (clearer) photo of the finished blade as to me it doesn't look much different in the second photo and I'm interested in seeing the results

I like the sound of the valve paste, might just have some lying around.....

 

[woodbloke]

Tony - hope you can see this a bit better. I spent another 5 mins on the DMT stone to get it like this:

Sorry for any reflections but it's a bright day and shot in the w'shop without flash on a macro setting - Rob

 

[DaveL]

Rob,

OK so I have never made a plane blade, :roll: but having made a few punches and scriber's, (while at school) I remember doing most of the shaping before hardening and tempering.
So would it not have been better to file a bevel on the blade before heat treating it? :-k It would of course still need grinding but most of the metal would have been removed by the file while soft. 8)

Nice polish your working up on the back. \/

 

[woodbloke]

Dave - in our discussions with Newt, he found that manufacturers do indeed grind the primary bevel before heat treatment which then causes the blade to go slightly concave when the heat is applied so there is more work needed to fatten the back, not less. With the blade fully hardened and tempered as in my pic, it only takes about 10mins on the Tormek to grind the primary bevel - Rob

 

[Alf]

I can see I'm going to have to try the grinding paste again. I gave it a shot some time back and wasn't grabbed at all, but can't remember why #-o

a small quantity of 45g diamond paste, mixed with a little paraffin to form slurry.

It's probably worth mentioning that I used a little less than I would normally, especially the paraffin, because it was going to have to get packed up to travel and I didn't want to loose more diamonds/make more mess than necessary, so perhaps that would account for some of the speed. Mind you, if I'd known someone-who-shall-remain-nameless was gonna wipe them off anyway #-o :wink: I'd have probably used even less... :lol:

With regards using a belt sander, you can actually lessen your work on extreme cases of blade-back-bother but it requires a bit of skill in only removing where you want it - not self-jigging at all. IME a blade has to be in serious bother to make the effort worth while and even then you're still looking at subsequent work anyway. But it can be done.

Cheers, Alf

 

[woodbloke]

Alf wrote:

Mind you, if I'd known someone-who-shall-remain-nameless was gonna wipe them off anyway I'd have probably used even less...

That'll be me then . Seriously Al, I wiped them off from force of habit (as I said on the day) as you need to keep clearing the slurry from the DMT stones...apologies again but thank you very much for showing us that method, it certainly do save a bit o' time - Rob

 

[Woody Alan]

I have been following this thread with interest and a couple of questions have cropped up. I used to be able to buy individual pots of grit from Axminster but can only find the lapping plate set with several grits. Am I confused (more than normal that is ) is there another source for this besides the stone tumbling O/L's?
Secondly where do you obtain the diamond paste from at reasonable cost, as I would like to have a go at this method to compare with other methods I have tried.

Cheers Alan