Dubbing plane iron when flattening

[harlow]

I'm trying to flatten the back of a new plane iron with 120 grit sandpaper on glass but I keep dubbing the edge so could someone tell me what I'm doing wrong. I though it was because I've not stuck the sandpaper down but I've read people are having the same problem when they stick the sandpaper down.

 

[Roger928]

dubbing the edge

???

 

[harlow]

???

I don't know what's the proper name but I've just added a photo.

 

[Roger928]

Left hand corner?
No idea what that is without seeing it.
What make is the plane?

 

[Deleted member 174758]

Some thoughts off the top of my head =

It's almost as though you are putting pressure on that corner when you are flattening the back. Do you always lead with that corner? (Question based partly on the direction of the scratch marks). I have a tendency to make more of a fore and aft movement when I flatten chisel backs, although I use a diamond hone (which is basically a 5mm steel plate). Also, what thickness of glass are you using and what is beneath it? Your glass (which should be float glass) will need the support of a thick and inflexible piece of plywood or MDF if it is less than about 10mm thick - thinner gkass really can flex.

 

[Roger928]

Most window glass is float glass. I use safe edged toughened glass as my flattening and finishing surface.

 

[Deleted member 174758]

Most window glass is float glass.

Agreed, most new glass is float glass, however, until the mid-1980s that wasn't necessarilly the case. And there's always the possibility that the OP is using a sheet of recycled material. You never really know unless you ask. And the issue of support and flexing still exist, even with float glass

 

[SammyInnit]

Might be better to use MDF with diamond paste.

 

[harlow]

I'm using 10mm float glass resting on my hop up. That's not my plane iron in the photo but it's the exact problem I'm having so maybe I'm using to much pressure. What diamond plate do you use as the two I have are rubbish.

 

[Roger928]

I use the DMT double sided diamond plate.
Then 1200 and 2400 grit on glass. And finish off with the Charlesworth ruler method.

 

[Roger928]

That's not my plane iron in the photo but it's the exact problem I'm having

How do you know its the exact problem?
Now that you've revealed its not your plane iron I can give my opinion on the dark spot.
Which is most likely a "heat spot" caused by a machine.

 

[harlow]

How do you know its the exact problem?
Now that you've revealed its not your plane iron I can give my opinion on the dark spot.
Which is most likely a "heat spot" caused by a machine.

The dark spot is blue marker pen from where the iron is dubbed over and the sandpaper is not touching. Have you got a link to the grit you use.

 

[Roger928]

Then its a low spot. A twist in the iron? Bad quality manufacturing machining?
Probably a low cost iron. Chinese?

Axminster sell the DMT plates. 10" x 3".
Mine is double sided. Fine and coarse. Not sure what grits but it does the business.
How much did you pay for the plane?

 

[Deleted member 174758]

Might be better to use MDF with diamond paste.

The problem with that is that MDF is really very, very soft so a combination of the lubricant in the paste wetting the MDF and the softness that nice flat surface might last as long as 30 seconds..... To grind steel you need an abrasive and ideally a lubricant of some description (to carry away the swarf and to prevent clogging) so that makes float glass or a flattened steel plate two of the best grinding surfaces

I'm using 10mm float glass resting on my hop up. That's not my plane iron in the photo but it's the exact problem I'm having so maybe I'm using to much pressure. What diamond plate do you use as the two I have are rubbish.

I use ITS diamond hones. Relatively cheap but serviceable without costing an arm and a leg - after all joinery isn't keyhole surgery, is it! I use a paraffin-based industrial lapping compound to "float off" the swarf and keep the diamond surfaces clean (never, ever use water - it encourages rust) - real paraffin will do just as well, but is an awful lot niffier. Note that you don't need to flatten the entire back of the iron - the bottom 1 to 1-1/2in up from the cutting edge is sufficient. You can check the cutting action by wiping the iron clean, blacking the back with a large chisel tip marker then doing your flattening. That will tell you what isn't flat (it shows up as still black) - and not all plane irons are flat. The process can be repeated several times but that 120 grit alox paper you are using is fairly slow working, so if after the first couple of strokes you have an unground area it may be that you need to use a coarser grit to get it flat first.

If you go away and do that and come back an post a photo it may be possible to tell you where things are going wrong

BTW, what is the history of the iron (new. old, been flattened before, first time, etc)? Is this the first time you've ground it? What grit did you start with?

Edit: There have been additional responses whilst I was writing this, so, it looks like the cutter has a thin spot. The only way to deal with it is to use a coarser grit (say 40 or 60 grit in a carborundum or silica carbide paper) and flatted with that first before working up through the grits.

 

[harlow]

Bad quality manufacturing machining?
Probably a low cost iron. Chinese?


How much did you pay for the plane?

The plane iron is made by ray iles and I think it was about £25 new.