Machine Stitching A Curve

[the deacon]

Hi all,

I've machine sewn many things in fabric and have done a fair amount of hand stitching leather. I've recently tried my hand at machine stitching leather. One of the challenges I've been having is setting a straight piece of leather into a curved piece.

What are the best practices when it comes to this? As you can see from the photo I've clipped and stitched like I do when stitching fabric, the difficulty I'm having is making sure my clipping does not disrupt the integrity of the leather, but is close enough to the seam line to achieve a clean curve.

I'm working with 4-5oz chromexcel leather for bags

Any help would be most appreciated.

Thanks

[TinkerTailor]

Glue. You use contact cement to cement the edges together, and then stitch, no notches necessary.

This is much stiffer than chromexcel, it is 4-5 oz veg-retan latigo and i was able to do these externally, which you could not do with notches(darts):

[BondoBobCustomSaddles]

First, those are called "darts" in the seating industry. The leather seating in vehicles have lots of them in the patterns, that is how it is done in production, you just have to be careful not cut into the area stitched. Second, as for what Tinker says, he is right, you are not doing "production" and can spend the time to glue and stretch around the corner before stitching. Just what you are comfortable with.

Bob

[TinkerTailor]

I should also mention that chromexcel is not the easiest to glue, especially grain to grain. The waxes and oils can mess up and resist glue. Surface prep by scuffing is the key to any good glue joint. Veg-tan glues easy compared to chromexcel. Practice and be prepared to change glues

You need real cement for this leather.

I use Lepage blue heavy-duty contact cement and it works. Get it at the hardware store. Others have had failures with most of the lesser glues sold at tandy when working with chromexcel. I like low smell glues for everything that I can use them for, however in some situations, "It won't stick if it don't stink".

In the USA i think it is weldwood blue they use. It is the same as the lepage i use.

They also make basting tape, a double sided tape, which some use for leather seams. Tandy sells it. Have not had good luck with it. It is not strong enough and the seam can separate during stitching leading to messed up projects, or after stitching exposing gummy tape balls...

[the deacon]

Beautiful work TinkerTailor, the image helps.

Interesting, in soft goods manufacturing "darts" describe the take up of excess fabric to shape, thanks for the heads up.

Also thank you for the pointers to use glue. I was under the impression in order to get a clean flat seam when you machine stitch leather right sides together malleting the seam open is necessary. How can this be done if the seam allowances are glued together?

I have some Master contact cement that shoe makers use which has worked well. Stuff is mighty powerful smelling though.

any tips on the best way to stretch and manipulate the leather around tight curves? In the fabric industry we use thinner seam allowances (1/4") around curves to facilitate smoothness, would the same apply here?

[TinkerTailor]

Beautiful work TinkerTailor, the image helps.

Interesting, in soft goods manufacturing "darts" describe the take up of excess fabric to shape, thanks for the heads up.

Also thank you for the pointers to use glue. I was under the impression in order to get a clean flat seam when you machine stitch leather right sides together malleting the seam open is necessary. How can this be done if the seam allowances are glued together?

I have some Master contact cement that shoe makers use which has worked well. Stuff is mighty powerful smelling though.

any tips on the best way to stretch and manipulate the leather around tight curves? In the fabric industry we use thinner seam allowances (1/4") around curves to facilitate smoothness, would the same apply here?

Flat or even french seams on a curve where you separate the layers and lay them flat are extra difficult........Tape may be the key here, as it is removable (even the permanent stuff. Not without a little damage to the material, but it comes off.) You could also do hand stitched "tacks" around the corner on the stitch line that you can cut out later after/while you make the complete seam with the machine.

IMHO the tack method should be saved for the most difficult areas as it is a PITA......

Edited February 4, 2016 by TinkerTailor

[Ole South]

Glue is your buddy when dealing with chrome tan gussets... and roughers, abrasive paper/cloth and denatured alcohol or sometimes acetone is glue's best friend. Thin leather will stretch more than most fabrics. Just clamp (lots of binder clips are handy) be patient and let set. If you're using real contact cement (Barge, Lepage, Weldwood etc) remember it is "impact activated" I.e. Use your mallet or hammer to set the seam then clamp.

[Ole South]

"Clean flat seams" Leather joining as in fabric seams have different construction methods. A flat felled seam is different than a French seam than a lap seam. Since we don't have to deal with "fraying" in leatherwork it's hard at first to set aside years of (woven material) "best practices" and embrace simplicity (and then NEW complexities arise) What is pictured isn't a flat seam it's basically a lap seam of the same facings (i.e. right side to right side or wrong side to wrong side) To belabor the obvious... Gluing replaces straight pins. Sometimes.

The example of the French seam is one of those "sometimes". Sometimes you CAN glue parts of a French seam (and use basting tape too!) Uwe just posted a great video of doing a two basic parts of the French seam.

The methods aren't so different... the medium IS.

[the deacon]

Thanks Ole South and everyone else.

Making the move from wovens has proved a touch difficult. Here is an image of a few woven seams and their names. Not pictured is the basic straight stitch (right sides together with a single stitch) or the french seam (where the edge of the seam allowance is encased in the seam allowance, so no fraying edges show). It seems terms like french seam and lapped seams mean something different depending on if one is using wovens or leather. I will take your advice Ole and embrace the more simplicity of leather stitching.

I am going to do more experimentation using the glue and clamp method and check out the results. What little machine leather knowledge I have came from a garment leather worker who used thinner lambskin. It was he who said to glue the seam allowances open after stitching to attain a crisp, clean seamline. It appears that advice mainly pertains to those thinner weight leather?

What are the pros and cons to using 1/2" seam allowance vs. 1/4"?

Thanks for the great discussion all.

[Ole South]

Seam allowance... depends on the material/design. I like 3/8", it allows for double needle look, lots of glued contact and 1/8" spacing, 1/4 gives similar look with a single stitch line. For me it's really what looks right and how much stretch/compression the material affords before puckering. Mallets are a tremendous aid in the disciplining of canvas and leather as well as setting the stitch line in both. I understand prior to hot iron they were used in the tailoring of regular fabric too. One more nice thing about leather is that it compresses better than most wovens thus a smaller seam doesn't force you to cut relief snips to keep the bulk down. Kinda cool to always have selvage too.

I just did an apron design that's horrible in light nylon (ripstop weight) but was easy in leather.

I couldn't gouge the seam lines in the body due to the type of leather used (waxed suede) and I'll probably use a contrasting thread if I do another in this color but... I was out of 138 black at the time.