On the Thickness and Making of Washers.

[miker]

A question in two parts, the first part WHY, and the second
part HOW?

I read an article in MEW (Model Engineers’ Workshop) titled
“An Introduction to Milling”.

In relation to setting up the milling vice, the author wrote
“ Use the correct size tee slot nuts and bolts for your machine.
Use a heavy flat washer of at least 5mm thick as a minimum
under the clamping nut and do not over tighten the nut”.

In another article in a different issue by a different author, also
regarding fixing things to the mill table, “The shortest studs
in my set are too long for some vices and fixtures so I often
use M12x30mm Allen head HT bolts with a home made
10mm thick x 20 or 30mm washer to increase the head
size. These washers help to bridge the oversize slots in
some fixtures aimed at the Bridgeport market.”

My first question, the WHY concerns what determines
the thickness of the washer?

Does the washer simply have to be thick enough not
to distort/bow under the clamping pressure?

Are two 2mm washers stacked on each other the same
as one 4mm washer?

Now the HOW?

What are some of the methods of making thick washers?

I seem to remember reading somewhere that one method is
to turn the outside diameter required and then use a parting
tool to cut grooves at intervals for the required number of
washers. These grooves would go to a depth so that when
you drilled the centre hole from the tailstock, the drill would
break through the grooves and the washers would end up
sitting on the drill.

I guess the faces of the washers would have to be cleaned
up somehow!

How would some of you do it??

 

[Deanofid]

Hi Mike;

Does the washer simply have to be thick enough not
to distort/bow under the clamping pressure?

Are two 2mm washers stacked on each other the same
as one 4mm washer?

Part of what determines the thickness is the size of your machine and the screws/nuts that you'll be using to clamp your work. Obviously, you don't need a washer nearly a 1/4" thick if you're clamping a 2" vise to a mini mill.
One thick enough to remain flat when you tighten your fasteners should do the trick. It needs to be large enough to bridge the slot, and give fairly good coverage of the top of the clamp, but it doesn't need to cover the entire width of the clamp.

Usually, two washers to make up the thickness you want would be just fine. As long as they don't bend when you have the fastener as tight as you want it.

What are some of the methods of making thick washers?

I think you could do it okay the way you have in mind, but it may be easier on the drill bit if you drill the hole first, then part them off like so many donuts.

To clean them up, you could use a pot chuck, or a split collet with an interior rim that would only allow the washer to go into it a given length. Then face them off.
I don't know if a pot chuck would be very economical for making just a few washers, but would sure work dandy. A split collet could be made for less than a dollar using a short piece of scrap round stock, and that's what I would use.

Dean

 

[Blogwitch]

Miker,

I am one of those people who doesn't play about with making t-nuts and their relative studs and nuts, except in exceptional circumstances where there isn't a commercial item available.

The correct ones can be purchased for very little outlay from most good tooling suppliers, and the nuts have built in washers to spread the load.

http://stores.shop.ebay.co.uk/Glost...796QQ_sidZ26428065QQ_trksidZp4634Q2ec0Q2em322

I am sure you can get the same thing in the US or in fact, anywhere else.

I know it is good to make your own bits and pieces, and save a few bucks in the process, but when it comes to major equipment mounting, vices, rotary tables etc, I personally consider it a no-no.

I have seen the results of some bodge up holding fixtures, and when it comes to having a ruined table on your mill or the outlay of a few bucks, there is no argument.


Bogs

 

[miker]

Hi Dean, thanks for the reply.

On the split collet, I take it that would be a piece of bar bored/drilled to the diameter and depth of the washer with a few slits
to allow it to compress. Would you hold this collet in a normal 3 jaw to use it or would you need a closer through the spindle?

Bogs, thanks for the input. I do have the full clamping set in red holder. Just wanted to know more about washers. ;D

 

[rickharris]

Just my understanding of washers and their reason for being:

The washer has 4 main functions:

1. To spread the force provided by the nut and bolt. This requires that the washer is stiff enough to withstand distortion and will depend on the force applied by the nut and bolt.

2. To protect the surface being clamped. for this the washer must be a suitable diameter and able to withstand the compression force applied. Materials and thickness should be suitable.

3. To provide a smooth surface so that the nut/bolt can be tightened to a consistent torque independent of the state of the surface being clamped.

4. To provide a counter force to discourage loosening of the bolt. The thread is an inclined plane (a slope) when torque is applied to the bolt it stretches - this applies a force in the opposite direction that tends to force the nut back up the slope (thread) thus loosening the grip. Generally friction resists this force but under vibration the friction can be overcome. There are many different kinds of washer (spring, Star etc) to provide extra force to resist loosening. Even a standard flat washer will provide friction to the understand of the nut and resist loosening.

Oh and a 5th reason - if washers cost 1 cent and a manufacturer fits 100 to a piece of military hardware they can charge another $10 for them!!!

 

[bob ward]

Are two 2mm washers stacked on each other the same
as one 4mm washer?

If the washers are purely packers then yes, if they have to resist bending, eg they are bridging a slot, the answer is no.
In general terms, the stiffness of a part that has to resist bending is related to the cube of its thickness.

So looking at the relative stiffnesses of 4mm and 2mm washers we have 4x4x4=64 versus 2x2x2=8, ie the 4mm washer is 8 times stiffer than the 2mm.

Two 2mm washers will be twice as stiff as one 2mm washer or 1/4 the stiffness of a 4mm washer.

 

[Stan]

I have a Benchmaster mill which uses 5/16" studs and non-standard T nuts. I was able to buy the proper T nuts but was stuck with 3/8" clamps. I made a bunch of shoulder washers out of 3/4' round bar with a 5/16" hole and a shoulder that is a snug fit in the clamp.I made similar washers to fit my vises and rotary table hold down ears.

 

[Deanofid]

Hi Dean, thanks for the reply.

On the split collet, I take it that would be a piece of bar bored/drilled to the diameter and depth of the washer with a few slits
to allow it to compress. Would you hold this collet in a normal 3 jaw to use it or would you need a closer through the spindle?

Bogs, thanks for the input. I do have the full clamping set in red holder. Just wanted to know more about washers. ;D

I think you have the idea, Mike. You can do this fine with a three jaw. You should need only one slit completely the side of the collet.

Just to be clear, I make them like this:
Chuck up a piece of round stock and drill it through. If needed to get the proper ID, bore until you have it slightly smaller than the piece you want to hold. Then bore the outer end so there is a recess that will just allow your work piece to slip in without slop, and deep enough so the workpiece sticks out far enough for facing.

When that is done, mark it so you put it back in the chuck the same each time, then take it out of the chuck and make one slit along its length at a place that will be between the jaws when you put it back in the chuck.

Put it in the chuck with your work piece in it, and tighten the chuck.

I use these for holding flat round pieces like small clock wheels and thin gear blanks that are hard to grip in the regular chuck. I think it's a pretty common work holding thing.

Dean

 

[Lew_Merrick_PE]

When that is done, mark it so you put it back in the chuck the same each time, then take it out of the chuck and make one slit along its length at a place that will be between the jaws when you put it back in the chuck.

Try this alternative: Drill a "stop hole" of a diameter at least 2X the kerf thickness of your saw blade (bandsaw assumed) approximately 75% of the OD of your collet along your "clamp line." Slit through the "long way" (i.e. across the 75% of OD). This will be more flexible and close on your washer OD more cleanly. I would then mill or file a screwdriver slot in the opening of your saw kerf for those times when the collet does not want to open for you so you can "encourage it" with a pry-bar (screwdriver that is essentially scrap).

Make the center hole in your collet 1.5 to 2.5 mm (1/16 to .100 inch) larger than the ID of your washer. In a real pinch (i.e. a gorilla tightened the chuck), you can get a punch through from the "back side" to save your part.

This IS the "voice of experience"...

 

[mklotz]

Let me add just a bit to this discussion of custom collets.

Keep the collets you make - even those needed for a one-off job. It's amazing how often one reuses them. Mark their size on them with a vibratory engraver.

When I make custom collets, I make them in the shape of a top hat. The "brim" prevents the collet from sliding into the chuck when mounting stock.

 

[miker]

Rick[/b], thanks for the synopsis on the purpose of washers.

I think it is easy to just whack a handy washer on something without giving
any thought to the exact function required of it.

Bob , I wasn’t aware of the “Cube Rule”, which you explained In a way that even I could understand. Thank You!

Stan, I have recently aquired an old Australian made Hercus Horizontal mill with
odd size T slots and will have to make T nuts and fixings.

The “shoulder washers” you describe, sound just the shot for using the clamping kit I got with my new RF 45 clone vertical mill.

Dean, thanks for the detailed explanation on the collet. That helps a lot!!

Lew, Thanks for the alternative method.

Does the slit still go completely from end to end of the collet, passing through the “stop hole”?

Marv, the idea of a “brim” or shoulder to stop the collet sliding into the chuck
really makes sense. Do you put the “brim” right at the beginning of the collet
tailstock end, or in a little way towards the headstock end of the collet?

I really appreciate the replies and great information, particularly on what at first might have appeared to be a rather mundane topic. :bow:

Dean, Lew, Marv, a photo or two of your collets would help me, and others might
appreciate also.

 

[Lew_Merrick_PE]

Lew, Thanks for the alternative method.

Does the slit still go completely from end to end of the collet, passing through the “stop hole”?

Yes, it is a stress relief that allows the entire collet to "pivot" closed more than just a thou or two as an unslit collet will.

I will see what I have in the way of photos. I have not posted any here and I will have to figure it out.