Teflon Washer For Coil Bolt/nut - May Help Ear Breaking Problems

[PimentoUK]

One thing I notice with my Equinox coil fixing bolt/nut is that it's very stiff to turn. I assumed it was mostly friction, and not much to do with applying compression to the clevis washers and coil ears. It makes no sense for it to be that stiff, when the coil ears are vulnerable.

So I decided to experiment with some PTFE/teflon washers underneath the head of the bolt and nut. These are cut from a thin sheet of PTFE-coated glass fabric. My sample came from the composite industry, Tygavac branded stuff that's used when autoclaving glass/carbon fibre items. However, it's widely available these days for a variety of less exotic uses, including heat-sealing. There's sellers on eBay offering small quantities at low prices. Some sell 10cm square sample pieces for a dollar or two. Search for:

"PTFE heat sheet" or "heat press sheet"
and look for brown-coloured stuff.

Cut it out using a sharp knife and scissors. I stuck on some masking tape, so I could mark out the cutting lines easily. A pair of compasses could be used to draw two circles, or use the nut as a template to draw round.The central hole is 8mm ( it's an M8 thread ), outer diameter is 27mm.

You really only need one washer, under the nut, if you can ensure you don't tighten the bolt, only turn the nut ( my recommended practice ). Nut and bolt heads are near-indistinguishable, so, if you pass the bolt through from the cable side of the coil, then the nut will always be on the easily accessible non-cable side.

Does it work ? Yes, there's a big drop in friction, I actually feel like I'm tightening the bolt, rather than just wearing away plastic. I'm sure I am less likely to over-tighten the bolt as a result.

Attached picture of my set, for guidance.

[sodbuster]

Great Idea.   Thanks!  I'll be trying this one out.

 

Is this the right stuff?  Ebay USA 

https://www.ebay.com/itm/403268989722?hash=item5de4b4731a:g:ZoUAAOSwQCNhf0aU

[PimentoUK]

Yes, that's the stuff. But a quick scan of eBay USA suggests small quantities/samples are not available, the cheapest seller I could find listed at 7 Dollars ( plus a few direct-from-China listings ).
There is an alternative, that should be OK : toaster bags. Try searching for:
"toaster bag" ; "toastie bag" ; "toastabag"; "non stick toaster"; "grilled cheese toaster"
These are often sold in small boxes or 2 or 4 ( in the UK ), very cheap:
toastie bags
US ebay:
toastabags US

They are likely something that you could buy in a store,( rather than online Amazon/eBay etc ), looks like a two pack for 3 or 4 Dollars should be possible?

The specs for the "50 times reuseable" ones state they're food-grade PTFE, and from the photos, they seem to be the same stuff; pale brown with a woven pattern.

[GB_Amateur]

A couple notes to add:

1) since both the bolt and nut have a recessed inner surface, an undersized washer won't do anything.  As such cutting a washer with an (slightly) oversized outside diameter wouldn't hurt.

2) 'Teflon' is a generic term which describes many different products.  I see you specified 'PTFE/teflon' (PolyTetraFluroEthylene) for your initial washer material which is the original teflon developed by DuPont back in the early 1950's.  It's usually white or off-white/translucent so I'm assuming those washer inner structure (you mention fiberglass) has the tan color. 

Are the sandwich bags made of PTFE or some other polymer?  May not matter as 'teflon' typically refers to a non-stick (low friction) surface.

An alternate (or additional) trick is to put a thin plastic washer (shim) inside of the ears.  When done properly this prevents the ears from being bent/torqued to the breaking point.  For my Equinox (which uses a modified X-Terra 705 shaft and gaskets), the stock (X-Terra 705) gaskets wear away with time which necessitates the shims.  I assume similar occurs with the stock Equinox gaskets but not sure about that.

[sodbuster]

I just bought some to try.  $6 including shipping for 3 - 16" x 20" pieces.   I'll be able to pass out a few samples when it arrives.

You could make a lot of washers out of a 16 x 20.    

[mn90403]

3 hours ago, PimentoUK said:

Yes, there's a big drop in friction, I actually feel like I'm tightening the bolt, rather than just wearing away plastic. I'm sure I am less likely to over-tighten the bolt as a result.

You address a situation that happened with my 3030 ears many years ago.  If you tighten the bolts too tight the friction is so great that it has a tendency to tear open the eye of the ears.  When you adjust the coil to the ground with a tap to make it level the hole can just open up and tear away from the rest of the ear.  This is what happened to me when my ears tore open from the friction rather than the force of compression.  You need the bolts tight or snug but not much more than snug/hand tight.  My big 17" coil on my 3030 when adjusted to ground with tight bolts ripped open the eyes.

That lesson learned, I don't over tighten my Equinox coils.  Tighter does not make it better but can provide an additional stress point for breakage near the coil itself.  It is for this reason I think that Minelab should have made longer more flexible ears that can withstand some user overtightening.

[PimentoUK]

The "toastabags" are described as food-grade PTFE in some listings, I've edited the post to show this.
Even a 10cm ( 4 inch ) square would make a fair few washers, definitely enough to share out with your detecting friends.

I've no idea why the sheet is 'envelope brown' ... my Tygavac sheet dates to the mid 1980's, and it's the same colour as that sold today.

One other possible washer material ( untried ) is polypropylene sheet. This is sometimes used for plastic bottles, like shampoo. Check your toiletries, kitchen cleaning products, etc for PP markings. This is a 'relative' of PTFE, and shares some of its slippery nature. A single washer cut from a bottle wall will fit under the nut without any space issues.

[phrunt]

Do you think these would work? Only ones I can find locally, cheap as anything though, almost free

https://www.mitre10.co.nz/shop/non-branded-toaster-bag-clear/p/161946

They're clear though so perhaps different.

[PimentoUK]

Hmm, the 'clear' ones seem different, and usually seem to have fewer use cycles.
Keep searching for the brown ones, probably these?

toastabags

gold toastabags

[midalake]

2 hours ago, mn90403 said:

Tighter does not make it better but can provide an additional stress point for breakage near the coil itself.  It is for this reason I think that Minelab should have made longer more flexible ears that can withstand some user overtightening.

For me personally in regard to beach hunting. I like my coil ears locked down TIGHT!