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TD3 SI Toe Bail Max Adjustment?


fishrising

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How far into the threads of the toe bail on a TD3 SI (long plate) can you safely go?  IE can you see some threads on the toe bail and be safe?

I’ve got new size 31.5 325s and had to make a full turn or two to maximize the extension of the to bail in order for my boot to fit.  I’ll check the sole length tomorrow.  But there are longer than my old Head Stratos Pro boots for sure.  Had to slide the toe bail out one notch on its base and lengthen the toe bails to the point where I’m a turn or two into the threads.

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I thought that looking at design criteria for aluminum-body turnbuckles might give some guidance.  For example, here's a product page for a turnbuckle with a 1/4-20 thread (similar in size to the 6mm thread on the bail😞

https://www.mcmaster.com/3003t17

Here's a drawing shown on that page:

turnbuckle.jpg.d72949a3df39209423e22f76378c9e70.jpg

Comparing the 2 15/16" length of the aluminum barrel to the 2 1/8" max. adjustment range, we can work out the length of the threaded aluminum section on each side [(2 15/16 - 2 1/8)/2] = 0.406 inches.  Dividing that 0.406 inches by the nominal 0.25 inch OD of the bolt, they have an aluminum engagement of 1.625 (call it 1.6) times the bolt OD.  Following this logic with the 6mm OD of the bail, you'd want 6 x 1.6mm of threaded engagement - 9.6mm engagement. 

Rounding up, you would want 10mm engagement of the threaded connection to match the turnbuckle design. 

Based on Lurch's measurement of 17mm of thread at 1 mm per thread, you could have seven threads not engaged.

Now for some disclaimers:  This is a cheap turnbuckle with a 60lb capacity sold as "not for lifting". You might want to go with an extra safety factor when using it as a model for the binding.  Also, on TD3s, if you accidentally step on the bail, the lug is constrained from moving so you will tend to mash the bail downward within the thread, possible causing the end threads in the lug to "trumpet" outward making those end threads less effective.  Another reason to maybe add an extra safety margin.

My gut feel is that having 2 threads showing probably does not weaken the threaded connection much as you probably still have 13 or so threads that are well engaged (with two more threads not well engaged at the end).  I wouldn't feel comfortable going much beyond that though.  Also, on any damaged bails I've seen, the bail snapped off at the end of the threaded section due to stress concentration, rather than pulling out of the aluminum lug.

 

 

Edited by Wolf
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"I'm a turn or two into the threads" has me worried but you also said " Can you see some threads ?" If the banjo joint on the toe piece has play in it (does it wiggle side to side when threaded on to the bail) i would want to maximize the thread count. The threads in the aluminum piece start further down the hole and this design does give some strength to the bail where the threads end on the bail and the smooth shaft starts. By exposing this area without support of the banjo joint is a weak point. Over time sloppy threads will strip away the aluminum. Check often ! Extending the slot under the aluminum bar on the metal heel receiver may be the better option .

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3 hours ago, fishrising said:

I'll take some pics tonight.  But all possible adjustments are "maxed" out.  Last step is micro-adjusting the toe bail.  I am 99% sure I have the long base plates, but if someone has a measurement for the actual length of the long plate, I can double check that against mine.

Here you go. I would be 99% sure you have long plates with M31.5s - I run M29 (BSL 319) and had to get long plates to center the boot.

DSC_0130.JPG

Edited by Lurch
BTW that new Tanker is sweet!
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I'll have to check my other pair of TD3s as well, but I am now thinking the pair I began to fit to my new boots are regular (short) plates.....ugh..... I recall taking note that the inner set of holes were right next to slots for mounting to the cant disk.  I know I requested long plates when I ordered them years ago, but since my Head boots fit in them I never questioned that I didn't get long plates...

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4 hours ago, fishrising said:

Little dremel work, wouldn’t take much...hhhhmmm

This will work, but you will  (still) have zero ability to center/offset your boot. Which might not matter. Or...

Edited by Lurch
Spchellin wuz rabbish
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So...here is where I landed only using the adjustability of the bindings.  I have not cut, grinded nor modified anything.  Thoughts on how things look?  Any concern on the minimal toe bail thread showing?  Any concern with how the heel is engaged?  Still might go after long plates.  But this might work for the interim.
 

 

0E70055C-20D2-483E-ABAD-079B6C14FBA5.jpeg

DDBDA7BB-08A8-434E-A2EB-E72358163D8B.jpeg

7D8538C5-8EEF-4E95-BD70-2FDACEF2B2AC.jpeg

87BB97B9-230F-40C9-8003-6C9699247162.jpeg

Edited by fishrising
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Looks within margins to me.  Since you're using the step ins with Fintecs you have an additional safety layer if the toe bail does break.  

All of my TD3 bails have always broken right where the threads end... knowing that I wouldn't do any traveling without spare bails and spare lugs and the correct sized allen wrench.  It's really difficult to get the broken bail end out of the lug especially at a resort.

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