Is B69 thread thick enough for use attaching bag handles?

[AEBL]

I made a bag (sort of a tote bag), trying to learn how to use my new sewing machine (Consew 206RB-3). It came with lots of B69 thread. I'm used to hand sewing with 0.6 mm tiger thread and this stuff seems like spider silk by comparison. Is it thick enough for reliable handle attachment? The sewn tab is 2 inches long.

Edited Sunday at 12:25 AM by AEBL
added sewing machine type

[Tigweldor]

Naturally that depends upon how much weight you plan to tote around in your bag.

You can always strengthen the handle attachment stitching by making a box X stitch.

Also it matters on how the rest of the bag is stitched - no use having a monstrous handle if the stitches fail at the bottom of the bag and it falls apart there.

 

Greetings

Hans

[AEBL]

Very true! But it doesn't seem like B69 was a poor choice, from what I gather? This is a prototype, I already warned the wife about it ...

[AlZilla]

Plenty of handbags are made on domestic machines with V69 or less. Unless it's a bowling ball bag, she'll be fine.

[kgg]

10 hours ago, AEBL said:

I'm used to hand sewing with 0.6 mm tiger thread and this stuff seems like spider silk by comparison. Is it thick enough for reliable handle attachment?

I guess it depends on how large the bag is and how much stuff it will be loaded with as well as your stitch length. It comes to a point where if your stitches per inch are to small the seam will act like a perforated paper tear off strip like you see with a cheque book. 

As a comparison the V69 you used to attach the handle has a breaking strength of 11 lbs and is about 0.012 thick versus the 6mm thread you are use to having a diameter of 6mm and a breaking strength of about 50+ lbs.

If you want to use thinner thread as V69 is really in my opinion a domestic size thread. Typically the domestic sewers refer to that size, V69, as heavy duty as it is the largest size most domestic sewing machines can take. I would move up to V92 with a breaking strength of 14.5 lbs and probably a stitch length of 6 stitches per inch.

As a note:

i) B69 is basically the same as V69, Tex 70, M40, Tkt 40, D236/3 just a different designation standards. In North America the two typical standard ways of referring to a thread size is either by the US designation, " V " and in Canada the metric " M " and the US " V " designation.

ii) The Consew 206RB-3 uses system 135 x 17 x (needle size) needles for fabric and 135 x 16 x (needle size) needles for leather. When sewing leather use the 135 x 16 x (needle size) appropriate for the size of thread.

Here is a good cross reference chart for thread size and the corresponding needle size that should be used. ( https://www.tolindsewmach.com/thread-chart.html )

kgg

 

[AEBL]

Thanks for the info! (and CowboyBob's chart is great)

Edited Sunday at 12:51 PM by AEBL

[AlZilla]

Here's a dissertation on seam strength:

https://www.sailrite.com/How-to-Sew-Webbing-Loops

Sailrite says "Stitches Per Inch x Breaking Strength x 1.5" = Seam Strength Per Inch

I think your wife's handbag is going to hold up.

[kgg]

7 hours ago, AlZilla said:

Here's a dissertation on seam strength:

https://www.sailrite.com/How-to-Sew-Webbing-Loops

Sailrite says "Stitches Per Inch x Breaking Strength x 1.5" = Seam Strength Per Inch

This formula can very misleading as it was develop mostly for fabric and indicates that by increasing the number of stitches per inch increases the seam strength it leaves out the practical factor before you damage / weaken the material, fabric or leather. As a note the strength factor would be 1.7 if you were using a Chainstitch machine.

Using the formula in that article for Lockstitch machines:

i) 6 stitches per inch x V92 having a breaking strength of 14.5 lbs  x the strength factor= 130 lbs / inch

ii) 20 stitches per inch x V92 having a breaking strength of 14.5 lbs  x the strength factor= 435 lbs / inch

The stitches per inch is stitch density and for leather it is recommend the stitch density should not be more then 3 to 4 per cm which converts to 6.35 - 8.46 stitches per inch.

The reference article for this is Schmetz, Sewing Focus Technical Sewing Information -- Section 3.3 ( https://www.schmetz.com/mm/media/zh/web/7_tochtergesellschaften/bilder_18/schmetz/pdfs_4/sewing_focus/SewingFocus_20_3075-22_Lederbekleidung_D.pdf )

kgg

[AlZilla]

As a practical matter, I believe the strap is going to stay safely on the lady's handbag.

[AEBL]

She'll be happy about her bag being safe-ish for lugging all of the stuff she lugs around, for sure.

I'm seeing how much of an engineering problem this is ... and I'm liking it more. Makes me want to set up some stitch samples and a set of weights and take some failure data. I'm sure it also depends on tannage and thickness somewhat. Very neat.

[kgg]

11 hours ago, AlZilla said:

As a practical matter, I believe the strap is going to stay safely on the lady's handbag.

I do agree.

8 hours ago, AEBL said:

I'm seeing how much of an engineering problem this is ... and I'm liking it more. Makes me want to set up some stitch samples and a set of weights and take some failure data. I'm sure it also depends on tannage and thickness somewhat.

To name a few variables the results will depend on:

i) leather type and thickness, chrome vs veg tan

ii) thread size

iii) thread type, nylon, polyester, etc

iv) needle size and tip shape

v) stitches per inch

vi) stitch patterns

About a month or so ago I got a new metal lathe, We had to move the wooden crate from the driveway to the rear of the house about a 60 foot or so move. We used my little 25 hp tractor using chains wrapped around the crate and hooked to the bucket hooks. No problem and in the basement we used a 1 ton shop hoist, 600 lb capacity hydraulic table and a combination of 2" and 3" nylon lifting straps. I always use backup straps as a just in case. One of the lifting strap on the last lift failed at the seam stitching of one of the end loops. It took the weight initially then went off like a gun glad we had the backup straps on or it could have been a bad day.

kgg

[MarlinDave]

Similar question. Brother in law has a firewood carrier, synthetic eth web handles. Wants it remade with leather. Making it out of chrome tan, gonna contact cement and stich carry straps with 138. Do I need to add rivets too? Figure it will carry 50 to 60 lbs firewood. 

[AlZilla]

8 hours ago, MarlinDave said:

Similar question. Brother in law has a firewood carrier, synthetic eth web handles. Wants it remade with leather. Making it out of chrome tan, gonna contact cement and stich carry straps with 138. Do I need to add rivets too? Figure it will carry 50 to 60 lbs firewood. 

As above, do the math. An X or W pattern helps add stitches, if you need them.

I made mine from pig suede. I wrapped webbing all the way around and sewed it with v138. I used maybe 1.75 inch webbing. Essentially, the webbing carries all the weight anyway.

[AEBL]

@MarlinDave, like AlZilla said, for sure, do the math ... size your stitched area for ~ 50% more weight than you figure the maximum weight it should carry (a "safety factor").

@kgg, glad you had backup! I suppose another variable is "shock loading"