Washer bore sizes

[Parlo]

I'm referring to hole tolerance not the size of the hole. When punching off from strip, you have to worry about things like strip width, drift, twist, feed speed, punch speed, tonnage, etc. It isn't just about the size of the relative punch size that we need to consider here when determining cost.

Examples:

Precise punching requires close width tolerances so the web can pass through the die guides without drifting too much and not binding.
Loose tolerances require less setup time where as closer tolerances require more time.
Closer tolerances may require pulling more punches as the tool wears.
More tool changes either requires more sharpening, or more tools.
Don't want to sharpen as much? Get better tool steel = more money.
I could go on about oils for loose, fast punching vs. slower, precise punching.
Cleaning web oilers, rapid feeder settings, etc. require different levels of maintenance, changeover, operator training and settings.

In other words, different tolerances require different process parameters, even on the same machine.



This is absolutely true. If you get paid for scrap, and at the volumes you need to be profitable in the fastener world, you need to get paid for scrap or you are throwing profits away. To tie this to my assertion about cost. The amount of scrap you make depends on well your process is defined and how well you execute that process.

We have strayed off track, sorry to derail the conversation, but it is an interesting conversation because this not only applies to the humble washer, but to the most complicated assemblies you can imagine.

Punching requires precise tooling whatever size hole you are producing.
The piercing process will produce unacceptable burrs well before the hole size changes so whatever size hole hole you pierce the parameters are the same.
The process will either pierce the hole first then blank the diameter using a pilot to centre the hole. Or a compound tool that produces hole and O/D in one hit.
I expect the reduced tonnage required to pierce a smaller hole will compensate for a few thousandths of scrap around the hole slug.
With the same O/D punch and a smaller I/D punch - both still using the regular clearance on the dies for the material spec, the process is identical except for a reduced piercing and stripping tonnage.

 

[vtcnc]

Punching requires precise tooling whatever size hole you are producing.

That is not necessarily true. The precision depends on what clearances are required and the tolerances to the part print.

The piercing process will produce unacceptable burrs well before the hole size changes so whatever size hole hole you pierce the parameters are the same.
The process will either pierce the hole first then blank the diameter using a pilot to centre the hole. Or a compound tool that produces hole and O/D in one hit.

I'm not quite sure what this has to do with the topic at hand.

I expect the reduced tonnage required to pierce a smaller hole will compensate for a few thousandths of scrap around the hole slug.
With the same O/D punch and a smaller I/D punch - both still using the regular clearance on the dies for the material spec, the process is identical except for a reduced piercing and stripping tonnage.

Again, the process is defined by other factors as well. Speed, material quality, feeds, setup time, etc.

Since we are talking about the difference in cost between an M6 and 1/4" washer or close fitting washer of similar size, I was trying to offer some suggestions as to what could make up the difference in cost in small margin products such as these.

There are a lot of other factors as well. Another factor not discussed is demand or how the products are positioned in the market. Those affect price as well. Anyway, I'll stop, I don't think I'm helping with the conversation.

 

[extropic]

Does anyone know why there is clearance in the bore of a washer? There is nothing worse than the washer not concentric with the screw head on assembly.

I also don't like the sloppy fit of common hardware store washers. I work mostly with inch fasteners but have no reservations about selecting metric, mil spec (Military Specification) or special washers to get the fit/function I want.

One of the functions of a washer can be to provide enough radial and axial clearance for a fillet, at the fastener's shank/head intersection.
To avoid stress risers, the fillet should not bear on the potentially sharp edge of a hole. In days of old, bolts may have had larger, non-standardized fillets, so large clearance was needed to ensure function.

There may be historical (maybe ancient, LOL) that would explain the situation.

 

[Parlo]

That is not necessarily true. The precision depends on what clearances are required and the tolerances to the part print.

I believe you are referring to the shear/break ratio of the hole where a longer shear requires a tighter clearance and more tonnage to pierce and strip. The payoff is shorter tool life between regrinds but a better bore. Although, the smallest diameter ie. the shear portion will remain the same whatever clearance is used. That size is entirely dependent on the punch size.
Whatever clearance is used, alignment is paramount so my comment that precision tooling is required whatever clearance is used is required to maintain quality and tool life.

I'm not quite sure what this has to do with the topic at hand.

My comment referred to your reference to tool wear. Also the description of two possible processes especially referred to the fact that the strip width control is relatively unimportant as the progression tool has pilots to constantly pull the strip into the correct position. The same applies to a compound tool.

 

[Tozguy]

Does anyone know why there is clearance in the bore of a washer?

I just don't see the need for so much clearance, there must be a reason.

A loose fitting washer has always been an irritant for me too. The 'roast' might come as close to explaining it as we will get.