Cutting straight lines!

[Nelleyarm]

I am new to leatherwork, though not to sewing and construction with fabrics.   I understand the need for sharp knives.   I also understand that without straight cuts, it is pretty much senseless to try to put something together.   It seems I am, so far, totally incapable of cutting a straight line!  Multiple knives, roller cutter, fresh blades, scalpels, all tried.   The biggest challenges are leathers about 2-3 mm of different types.  Those of looser temper are most challenging.

A couple of questions about approach.  I prefer to stand, and have a sit-stand work area so can adjust the height.   Is it better to be closer to the work?  Does distance of upper body (being closer) help with application of pressure on the knife?  What is the best way to get a smooth continuous...and straight...cut?

One major issue is keeping the leather still and flat, and holding the pattern on the leather...one or the other always seems to move, even on short runs of 8-10 inches.  Longer runs wiggle more.  I have tried weights with limited effectiveness.  Do have self-healing mats and all sorts of rulers and straight edges and squares.

So that is the first area needing some input.  I see the pros and semi pros cutting giant pieces of leather perfectly straight by eye on You Tube.  Obviously some of the control will come with experience.   What are some other tricks?

The other major question is how to hide or fix mistakes...that one (or 10) crooked or out of line stitch, a hole in the wrong spot, those wiggly lines that need straightening.    Oh yeah, and how to keep hole punches from bouncing and making 2 impressions.

If any of you have suggestions, tricks, tips, videos, It would be grand if you could share a few on these areas.    Thanks!

[bikermutt07]

It drove me crazy in the beginning too. The leather would always stretch at the end of the corner giving that jut out of square.

Knives sharp enough for one pass is what I have found to work best. 

If you have a round knife you can roll thru the end of the cut and not cause the leather to stretch. 

Sand paper comes in handy for cleaning up uneven cuts, or even a Dremel sometimes.

These are my go to knives. They are all Knischield knives. I use the round knife the most. The curved detail knife is really handy for those tight spots. The bevel point knife doesn't get used much. But it is really awesome at cutting card pockets on thin flimsy leather. I can basically push the knife straight down chopping the line instead of cutting it with a stroke. 

I am a hobbyist and this is over 500 bucks worth of knives, but cutting has become so comfortable with them. I slowly collected them so the money wasn't missed that much.

If I could only have one it would the round knife. Followed by the curved knife.

Also I go around my templates with a scratch awl the cut them out. That usually works pretty well.

And I do use a rotary cutter on the long stuff.

As far as hole punches bouncing, you need something firm. Granite is what most of us use with a rubber mat or poundo board on top.

[brmax]

For the punch bounce, I found it required a real stationary table and or at the corner would help. CS osborne 603 cutting pad works great. I havent a clue what kinda vinyl rubber it is but it is in no way a mud flap or hard like hdpe. 

 

Good day

Floyd

[Stetson912]

Mutt has the answers. 

A hard dense surface for punching with something to protect your tools on to like mutt mentioned

A roller cutter will help with the stretch. Anything that had downward cutting or chopping pressure instead of more lateral or slicing cutting. 

Use multiple passes when cutting thicker stuff. Nothing wrong with that. Strait edges are your friend as well. 

[plinkercases]

As above, rotary cutters, head knifes, straight edges, clamps.

I have a 3x5x1/4 HDPE sheet on my cutting table so able to get a good continuous run at long straight cuts. and punching on 1" HDPE on about 3/4 granite on 3 inches of built up wood directly over a 4x4 leg to the concrete and for some tools all that with a poundo matt on top. and 2lb polly head mallet or maul.

Misplaced stitch you can remove and re-place right away with a careful placement of a new hole with the awl, wobbly lines (made with a creaser or round stylus type indent line) can often be smoothed with a modelling spoon/tool then done....hole in the wrong place.... bad... or adapt the design! use it in a new way or cover it or add one systemically off the other side of the piece and call it part of the design.

Welcome aboard and lets some of your work as you go.

 

[battlemunky]

One of those Olfa opaque quilting rulers helped me straighten up a good deal. Also, holding down your straightedge through the cut is imperative. Misplaced stitches happen from time to time but practice, practice, practice will tighten that skill up dramatically.

[VabaX]

dunno 'bout you, but I use a ruler....

[RockyAussie]

8 hours ago, Nelleyarm said:

 What is the best way to get a smooth continuous...and straight...cut?

The best way to get straight cuts so far other than perhaps a laser I do as below.  This shows a 100 shoulders to be straighten up to then run through a belt strip cutting machine.

Here I use a 1+1/2" x 1/4" piece of flat steel which I screw down to the table on one end and put a nail at the other end at the back behind the steel so I do not have to worry about it sliding away as I cut. I lift the steel and slide the leather under and drop it down again to cut. Note that there is a niko line under that shows me where the leather has to go past for cutting. The steel is flexible enough to follow and table irregularities.

With the back side of a sharp tipped knife I deeply scribe where I want to cut and then I position the steel back for the main cut. The steel weight helps to keep the leather still as well.

Here I like to use my round knife due to its edge holding up for generally most of the job. note at this stage I assist the cut by gently pulling the waste up and toward me.

8 hours ago, Nelleyarm said:

I also understand that without straight cuts, it is pretty much senseless to try to put something together.

Yeah I know what you mean. I just generally don't do it. Most of the time I design almost every thing to be first cut oversize and then be second cut when the pieces are attached together. That I normally do with made to shape cutting knives on a clicker press but sometimes by hand as in some of these pictures below.

8 hours ago, Nelleyarm said:

One major issue is keeping the leather still and flat, and holding the pattern on the leather...one or the other always seems to move, even on short runs of 8-10 inches.  Longer runs wiggle more.  I have tried weights with limited effectiveness

For cutting on a pattern which I normally print onto cardboard I start by printing the sheet and then spray gluing the sheet before cutting it out on my cutting table after the glue has tacked of well. These are often re glued and allowed to track off again before attaching to the leather I want to cut. This picture shows some pieces of a pattern spray glued and drying.

Here showing that even on very bumpy croc skin I can have the pattern hold still as I cut it or mark out for first cutting.

This one shows a pattern for the back of a bag being cut out.

Even on small pieces this method I use . I do hold it with my other hand normally but here I taking the picture with it.

This one below does not have the leather fully attached together as it has to have straps in it after the edging gets applied but again the tacky surface helps me cut exactly to size.

This is one of the finished bags of the patterns above. I have been trying to find time to post the full break down steps for it for some time but there are a huge amounts of pictures and words to do before that happens.

I hope that this is of some help to you and look forward to you posting some of yours in the future. Brian

 

[JerseyFirefighter]

I still would like to get an inside track on Springfield's cam and rail type cutter they use. I would buy one of those in a heartbeat. 

[battlemunky]

@RockyAussie, thanks for the above and that croc bag is quite awesome!