Outer Vs. Inner Presser Foot Spring Adjustments (Singer 111, Consew 206 Class)

[Uwe]

I posted this on another topic in the Sewing Leather sub-forum, but I think it also belongs here since it relates to sewing machines and applies to most walking foot sewing machines. Also to open it up to discussion without hijacking the other topic. Here's my original post (with minor edits):

Geek alert!

I've been giving this some thought because that foot pressure business has baffled me for a while and the inner foot spring setting never had any noticeable effect no matter how I adjusted it.

I've concluded that the inner presser foot spring has only little, incremental effect on how hard the inner presser foot presses down on the leather during the stitch cycle. Changing the spring or cutting a bit off will also have minimal effect.

This sounds weird and counterintuitive but the OUTER presser foot spring ALSO determines how hard the INNER foot presses down when outer foot lifts up. The pressure of outer and inner foot are NOT independent of each other, in fact they're closely and quite literally linked. This is because the outer foot actually uses the inner foot as leverage via linkages to lift up, against the spring that controls outer foot pressure. If you remove the inner foot entirely, the outer foot will not lift up at all because it needs the inner foot as leverage to press against the material in order to lift up.

I believe the main purpose of the inner presser foot spring is to ADD incremental pressure to the inner foot on top of what the outer foot spring already provides. Adjusting the inner spring will never allow you to lower the inner foot pressure below what the outer spring dictates.

I just now did a little experiment to back up my claim with some proof. I put a kitchen scale under my presser feet bars and moved the needle bar up so as not to interfere. I dialed the outer pressure foot spring low enough to get below the 10 lbs weight limit of my scale. I removed the inner presser foot spring adjustment knob entirely, so the inner spring was not pressing down at all.

With this setup and the inner foot spring totally out of play the outer foot bar pressed down registering 7.2 lbs:

and after turning the wheel a little the inner foot bar pressed down with 5.5 lbs:

The difference is likely due to linkage angle and lever lengths, but the two are proportional. If I dial up the outer foot spring pressure, so increases the inner foot pressure (all WITHOUT the inner foot spring involved at all)

Adding the inner foot spring control knob and cranking it all the way down for max inner foot spring pressure increased the inner foot pressure an additional 2.5 lbs over the initial value. This is the max the inner spring can ADD to outer spring.

The inner foot is also more likely to leave a mark because it has a much smaller footprint than the outer foot and exerts higher force per square inch with the same spring pressure (the skinny high heel of a shoe is more likely to leave a mark than the bigger front of the shoe, but your weight does not change as you walk.) So the small inner foot even at 5.5 lbs is much more likely to leave a mark than the bigger outer foot at 7.2lbs

I'd try dialing back the outer foot presser spring until it just barely holds on to the material when you tug on it and see if it makes a difference. Help guide the material with your hands as you sew to allow the machine to move the material easily and consistently with minimal foot pressure. Don't push or pull as it sews, just allow the machine to do the work with minimal force.

Sorry about the long and geeky post, but I hope it adds some clarity to this confounding foot pressure business.

[Wizcrafts]

Thank you Uwe for that research.

[LumpenDoodle2]

I was wondering about the inner foot adjustment. I've fiddled about with it a few times without it having any noticable effect.

[dikman]

Me too, I couldn't notice any difference when adjusting it. Now I know why. In my recent messing about with my machines, including re-adjusting all sorts of things, I re-adjusted the inner foot/outer foot settings and it took me ages to figure out what was going on - because, like you said, they're interlinked! I basically left it at that and worked out how to get the settings I wanted, but I admire your tenacity in working through this.

Another piece in the puzzle that is industrial sewing machines.

[Uwe]

The common naming of the two springs adds to or creates much of the confusion, I think. My topic title doesn't help either, come to think of it.

The springs and corresponding adjustment screw really should be referred to as big/major/rough adjustment for the big leaf spring in the back and small/minor/fine/incremental adjustment for the small coil spring because both springs affect foot pressure for both feet.

The big beefy leaf spring in the back of the machine provides the big/major/rough pressure. It changes pressure for BOTH feet by about 4 lbs (~2kg) of pressure with each full turn of the adjustment screw on my machine as measured by the scale.

The comparatively small and weak coil spring inside the head provides small/minor/fine/incremental adjustments for fine-tuning. It changes pressure for BOTH feet by about 4 oz (~100 g) with each full turn of the adjustment screw.

So if either of the feet leave marks, you need to adjust the pressure of the big leaf spring before fiddling with the small adjustment spring.

The generally smaller inner foot will show marks before the outer foot mainly because the inner generates a higher pounds per square inch pressure due to the smaller contact surface.

Most people can probably safely ignore the fine tuning spring adjustment knob entirely.

[spenzher]

This is great research! I know the two are linked, but I never occurred to me that they share the same pressure too. Good work! I was just wondering about this too, perfect timing.