Something's off, and I cannot figure out what exactly.

[HondoMan]

Right then, this involves cutting leather.  Yawn....  a wee bit of background. 

I have two rule stops in the shop.  One is 60cm long and the other is 30cm.  Both work well.  When I set the stop, I check it against another rule to ensure it's set properly.  
I also have two straight edges.  One is 100cm and the other 45cm. Equally solid tools and are incredibly straight.  Had all these tools for a number of years.

These lead to a rather odd problem.

Regardless of the leather used, this seems to occur often and oddly I haven't noticed it until a number of months ago.

Let's say I need to cut a strap 3cm wide.  I'll use either rule stop, set it, check it and mark the leather with a scratch awl in three places.  Left side, right side and the middle.  The marks are neither deep nor long.  I then set one of the straight edges down, line up the wee tick marks and the middle tick mark sits 2-3mm above the straight edge.  Again, regardless if I'm using 4mm vegtan, bridle, harness, or 2mm pull-up. 

Any of you lovely lot have ideas?  Anyone else encounter this issue? 

Cheers!

[Ddat]

Are you flipping your rule and there is a different scale on each side? I have a framing square that has imperial measurements on one side, then imperial marked off in tenths... If I'm not paying attention I'll get small mistakes like that.

[Northmount]

26 minutes ago, HondoMan said:

line up the wee tick marks and the middle tick mark sits 2-3mm above the straight edge. 

The edge of your leather is not straight.  It may be the way you lay it on your cutting table.  Clamp your leather down with its edge against your straight edge to make sure it stays straight. 

Or check your straight edges to make sure they are straight.

Use a strap cutter.

[HondoMan]

27 minutes ago, Northmount said:

The edge of your leather is not straight.  It may be the way you lay it on your cutting table.  Clamp your leather down with its edge against your straight edge to make sure it stays straight. 

Or check your straight edges to make sure they are straight.

Use a strap cutter.

All rules in the shop are straight.  I checked them when initially bought.  I learned that a donkey's age ago.  I don't think it's the table or how it's laid atop.

Aye, the 3cm example was poor.  For 3cm I will use the strap cutter unless I'm working with 1mm thick leather.  But still occurs when I'm cutting 30cm leather.

This is merely an odd matter I'm trying to get my head around.  It's not causing major issues, just gets on my arse.

[Gump]

It's because a cow is not flat, and no matter how you try , it will always try to revert to its unstretched natural lay. When you lay out a side, the outer edges will always have looser lay than the center of the hide, and when you flatten it with a straight edge, the ripples just move to a different part of the hide.

[dikman]

I've occasionally noticed the same thing, I put it down to leather being a natural product, as opposed to something that is manufactured and so has consistency. As Northmount said if it's an issue then clamping the leather first so it can't move helps.

[kirbytorres]

Have you checked if your leathers edge is straight, before measuring against it?

[Handstitched]

It does seem the edge isn't  straight . When I get my  new sides or shoulders etc. I have a long  straight piece of 2x1** timber that I use to cut a straight  edge with my knife  to then  start making belts using a strap cutter . The 2 x 1 is clamped down at both ends of the hide and sometimes in the middle.  If I don't do that  ' wonky' edges. Any off-cuts get used for small items , keepers  , book marks etc. 

**Other people will have different methods to start a straight edge . 

HS

Edited August 25, 2023 by Handstitched

[HondoMan]

Seems I need to add more to this.  When I'm about to begin cutting, I cut away the unusable edge with a straight edge.  The straight edges are not light and have a good weight.  So, I'm already working with a straight edge of leather.  If you're unfamiliar with a rule stop, it's basically a wee block of wood on a slide rule with a tightening screw.  Aye, it's made to fit the rule.  By no means fiddly.  Set the stop to the desired length.  Pushed against the edge of the leather and with the scratch awl, mark the leather.

It's understood that leather natural and sometimes have wrinkles.  I use old cast iron heavy irons to keep the leather flat or clamped down. 

All answers I've milled about in my head.  What is being overlooked folks, is that it is always...again always the middle mark.  The marks to the left and right are always spot on. 

[Gezzer]

My theory ...............   maybe your support table is not wide enough to support the hide ( assuming both ends are clamped and the middle is not )  # 2.......  or maybe your lighting in the center is giving a false  " on the mark "  I have had that affect a lot of things in carpentry work over the years .

Any way good luck figuring it out !!

[Burkhardt]

My guess is it's how you're cutting it and it's unavoidable. Strap cutters the leathers pulled straight through a vertical blade vs. pressing down and pushing or pulling a blade on the straight edge and the leathers stretching and getting it offline. I gave up on trying to get it straight and now use a straight edge and a pencil then cut the line instead of trying to cut against a straight edge. 

[Klara]

15 hours ago, HondoMan said:

What is being overlooked folks, is that it is always...again always the middle mark.  The marks to the left and right are always spot on. 

That is because you put your edge against the two outer marks. Two points define a line (basic geometry). If you aligned your straight edge with an outer mark and the middle one, then the second outer mark would be off. 

As for why the three marks don't line up, I have no idea. It has happened to me, but then I manage to make all measuring errors known to mankind and invent a few of my own...

[chuck123wapati]

On 8/25/2023 at 2:30 AM, Handstitched said:

 

**Other people will have different methods to start a straight edge . 

HS

i use a chalk line lol.

[chuck123wapati]

are you using something like this? How do you ensure that the edge your marking off of is straight and remains straight during the process?

[Frodo]

When you cut the edge the idles edge stretchfed

when the event happens again that you described, check the edge that you measured from. The center of your cut has stretched on you when you cut it

[Frodo]

1 minute ago, Frodo said:

When you cut the edge the idles edge stretchfed

when the event happens again that you described, check the edge that you measured from. The center of your cut has stretched on you when you cut it

When you use a metal straight edge the leather under the straight edge can move

it has been my experience that the middle portion of the straight edge does not get enough weight pressed in it

I personally am guilty on not pressing down in the center myself.  Buy a c-clamp

[Handstitched]

2 hours ago, chuck123wapati said:

are you using something like this?

I have one of those  Nowhere near as nice as that one. Made it in high school...way back when.... Our wood work teacher had one finger missing  ....good promo for wood work . So damn funny every time he pointed at us though,.... got some mileage out of that ,     LOL 

HS

[chuck123wapati]

Maybe you don't pull the ends as tight as the center when measuring. If you pull the center tighter and compress the leather a bit then when the leather relaxes back straight the scribe mark is farther from the edge or seemingly longer.