Need some help or advice with cutting inward curves (and using sandpaper).

[Amira]

Not sure that this is actually a "how do I do that" topic, but rather I need some advice. I'm really struggling with making decent cuts that curve inwards. In case you're wondering what I mean, take a look at an "S" for instance, on the opposite side of the outward curve there's an inward curve both at the top and the bottom. I have no issues cutting something round if it's outwards, but inwards I feel like I sort of have to use more force than I'd like - more force for me equals greater risk of cutting wrong or rather it just feels less precise and it is sort of fatiguing. 

The leather I'm currently using is veg-tanned, ~4mm thick, cow butt. I've tried: cobbler's knife, box cutter and surgical scalpels with different types of blades. Some works better than others, but none are satisfactory. So, any suggestion either about technique or a type of knife to try? Or is it just the nature of the beast? I suppose it doesn't have to be perfect as I could sandpaper to finish it off. Speaking of sanding, if you sand the edges of leather down and you want to glue several pieces of leather together, would you sand before or after putting them together or both before (more roughly) and after (just to align everything perfectly together)?

Any suggestion is highly appreciated. 

Edit: Or is it just a matter of practicing on making those kind of cuts more (i.e. lack of proper technique)?

Edited July 8, 2020 by Amira

[Dwight]

If I'm cutting rounded pieces . . . I cut a bit . . . turn the leather . . . cut a bit . . . turn the leather.  AND . . . I use a razor knife exclusively . . . nothing else.  Can't get confused that way as to which knife to use.

For sanding blocks of glued together leather  . . . glue first . . . then sand.  I have a 12 inch disc sander and a 30 inch belt sander. . . . they both do great jobs.  I make holster toes . . . bottoms for cell phone cass . . . bottom for special purses . . . 

May God bless,

Dwight

[Matt S]

Hi Amira,

These sorts of cuts are never easy. A lot will depend on the size of the workpiece, the temper of the leather and the size of the curve. I find a small. thin, well stropped, head knife the best for the job (Osborne 73 being my favourite as it sits easily against the heel of my hand with two fingers extended along the side of the blade). If you can't do it in a single pass give a shallow cut first, with just the very tip of the knife in the leather, then go over it again with the knife as deep as you can accurately follow the initial cut. Try to keep the knife in line with your forearm as much as you can and either turn the leather or turn your entire upper body from the waist if you can't move the leather.

You can do it with "pull" knives like box cutters and scalpels but I have always found that it adds a fair amount of extra difficulty.

Don't worry about going fast, that comes with practice. Concentrate on keeping the knife straight up and down, dead on your cut line, and moving steadily forward.

[Samalan]

Im with Matt on the headf knife i use a gomph pattern head knife it will cut 10 oz leather in one pass on round stuff like matt said do it in two the pattern knife is very narrow at the points also i have a knife used for chip carving that can cut a 1/4'' rad no problem very very SHARP is what you need or as some say "scary sharp" good luck.

[Samalan]

 On edge  sanding i use 80 grit open face for shaping, and finish with 120. For surface i rough it up with the back side of a lock back shaper cutter.

[mike02130]

Hej,

I use this for curves.  I make handbags and use this knife for cutting gussets and other curves.  It works great.  How big are the pieces you're cutting?   When I cut curves I have my piece on the table and cut with minimal wrist movement and turn with my body.  That way when you transition from inside to outside I don't rock or twist my wrist resulting in an out of square cut.  I also move the piece around to get the cut line in front of the knife.  Similar to cutting a figure out of paper with a pair of scissors.  One holds the scissors while moving the pattern. 

[zuludog]

Cutting inside curves is not easy. Try this method -

Mark out the line of the cut you want to make with a round awl, also called a scratch awl - that's how it got its name. This scratch will act as a guide for your knife

make your first cut very lightly, then firmer and firmer on subsequent cuts. Try using a clicker knife with a hooked blade, as shown by mike02130 above. You can buy these, and similar knives but with a fixed blade which you must sharpen yourself from www.georgebarnsley.co.uk 

For some inside curves you can use a round  strap end punch

For sanding I use 100 grit paper, either just folded over or folded round various shaped pieces of wood. Glue all the pieces together first, then sand them as one thickness

Watch YouTube videos of the kind of things you would like to make, and you'll see how other people do it; but sanding & finishing edges is is done for many items

What kind of things are you making, please? That might give us a better idea of how to advise you 

Edited July 8, 2020 by zuludog

[buzzardbait]

I always use a punch to cut the inside radius then cut from the hole with my round knife.

[jcuk]

Another vote for the Round Knife.

They can be a little daunting to some people at first but they are the right tool for that kind of weight of leather. There are some good Youtube videos out there on how to use and hold them correctly. 

There is a a knife called a single head knife which will do everything a Round Knife will do but a lot less daunting to use and easier to sharpen.

 

https://www.abbeyengland.com/barnsley-single-head-knife-552.html

 

Hope this helps

JCUK

 

 

[zuludog]

37 minutes ago, jcuk said:

Another vote for the Round Knife.

They can be a little daunting to some people at first but they are the right tool for that kind of weight of leather. There are some good Youtube videos out there on how to use and hold them correctly. 

There is a a knife called a single head knife which will do everything a Round Knife will do but a lot less daunting to use and easier to sharpen.

 

https://www.abbeyengland.com/barnsley-single-head-knife-552.html

 

Hope this helps

JCUK

 

 

You can buy the head knife from the makers https://www.georgebarnsleyandsons.co.uk

As a traditional maker they keep the cost down by only giving you a basic cutting edge; you must do the final sharpening and polishing yourself. However, once you've done that, it is excellent

There are several videos on sharpening round, and head knives; the same technique is used for both. JH Leather has a good video on this; also her videos show her using a head knife, though it is not by Barnsley

Osborne also make a head knife

[Spyros]

Ι will kinda go against the flow here, and I know many people won't agree with me, but don't buy more tools.  Trust your hand and your eye, and if you don't, keep practicing until you do.   It will give you confidence to do many things throughout this (and any) craft and it will often get you out of tight spots.  I firmly believe our hand-eye coordination is the most important tool and just like any other tool it also needs honing from time to time.

By all means try different things if it's easy and practical to do so but keep in mind that the perfect cutter might actually not exist.

Edited July 9, 2020 by Spyros

[zuludog]

37 minutes ago, Spyros said:

Ι will kinda go against the flow here, and I know many people won't agree with me, but don't buy more tools.  Trust your hand and your eye, and if you don't keep practicing until you do.   It will give you confidence to do many things throughout this (and any) craft and it will often get out of tight spots.  I firmly believe our hand-eye coordination is the most important tool and just like any other tool it also needs honing from time to time.

By all means try different things if it's easy and practical to do so but keep in mind that the perfect cutter might actually not exist.

Yes, I can go along with that as well

[johnv474]

Instead of a different tool, modify your leather.

If your leather is very dry, or less tanned, or dense, or if your blade is not sharp enough, it will be harder to cut.

You can get your leather damp with water, and that will soften it, but it takes too long to dry in my opinion. 

However, if you use hand sanitizer gel, which is alcohol-based, you can soften your leather temporarily.  Alcohol is used in lots of dyes, etc., so is used with leather already a lot.  The big advantage is that it dries much faster than water.

You will likely put a conditioner on your leather when done with your project, which offsets the drying effect of alcohol.

This is the fastest way to get better results that I'm aware of. 

[Amira]

First of all, thanks for all the advice and sorry for the lack of my replies to your feedback, the suggestions were really appreciated.

What I did was try talon-shaped scalpel blades, so they're sort of like the clicker knife shown in the first photo. They were a lot easier to cut with than the other shapes and tools that I used to cut with, as the leather gets easier to cut when you can cut the whole thing from the side through its entire thickness than cutting through the thickness starting from the top and going down (I'm sure that phrasing doesn't make a whole lot of sense). Might get a clicker knife when I feel like getting another knife to maintain (sharpen) properly. 

However I will heed Spyros' advice on practicing as well - as I am, after all, completely incompetent when it comes to crafts in general (mostly due to a lack of experience... or so I like to believe anyway), but cutting inward curves felt so much more difficult compared to other things that I felt I was probably doing something wrong.

Edited August 4, 2020 by Amira

[mike02130]

The clicker knife blades are replaceable.

[Rahere]

Also - anathema - consider bending your work over, removing the edge from proximity to the cut.