Fantasie 19
Well-Known Member
...which also ties you into buying from them and not making your own.... they aren't owned by Apple are they?
Autohelm / Tillerpilot extension thread specification - the definitive answer
- Thread starter winsbury
- Start date
...which also ties you into buying from them and not making your own.... they aren't owned by Apple are they?
anoccasionalyachtsman
Well-Known Member
I dropped in on a local engineers today, and we confirmed that Simrad use BSPP. We also went into his copy of 'Machinery's Screw Thread Book' and looked at all the weird and wonderful threads that might be associated with softer metals looking for any sign of the Autohelm dimensions and found nothing. He tells me that it's still fairly common for manufacturers to contrive their own (and says that Honda are the ones he comes across most often - on their Honda specific tools), so it's either one of AH's own invention, or something obscure like 'French BSPP'. (I'm only half joking, I've ordered a copy oh the book because it's a lesson in nationalism. Did you know that there's a British Metric, a German Metric and a French Metric - to name a few?
Topcat47
Well-Known Member
Honda have (had?) a nasty habit of using smaller hex nuts (af) than the ISO metric fine thread would suggest. This meant that a nut that accepted a 10mm socket wouldn't go on a Honda bolt with a 10mm af head. It's late and I"m tired so that's the best I can do, tonight.....
winsbury
Well-Known Member
My VW Passat has one particular bolt ( just the one out of 30 or so ) which needs removing to get the sump off, it's almost 17mm but not quite, turned out to be an imperial head with a metric thread, manufacturers huh, go figure !
Anyhow, I'm sending the pushrod to a machine tool maker and see if they can come up with anything. ie: Although I have it working now, I am not satisfied without having this nailed to the wall.
Anyhow, I'm sending the pushrod to a machine tool maker and see if they can come up with anything. ie: Although I have it working now, I am not satisfied without having this nailed to the wall.
earlybird
Well-Known Member
Pre-war Morris cars had metric threads with imperial hexagons. I had one.
colhel
Well-Known Member
Certainly when I made a couple extensions for my Raymarine TPs I machined a metric pitch on an imperial diameter. Can't remember the exact dimensions though
anoccasionalyachtsman
Well-Known Member
The chap I saw yesterday could do it but reckoned that cutting a decent thread internally would be better done with CNC.
I have an idea.
Buy a thread repair kit for 3/8 BSPP (Chronos do one https://www.chronos.ltd.uk/acatalog/info-HEL3819.html).
Repair your female thread in the steel rod, and then run a 3/8 BSP die down the thread on the alu extension.
And now you can use more Autohelm extension on the outer end, and Simrad ones on the inner. What's not to like?
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VicS
Well-Known Member
What I dont like is the fact that the wall thickness may not be sufficient to allow a Helicoil to be fitted.
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anoccasionalyachtsman
Well-Known Member
You make a good point Vic. I thought it was such a good idea too.
I'll wait for the copy of Machinery's Thread Book (ordered last night) and see if I can beat the OP's engineer to come up with a name for this thread. Whether a tap for it will available is a whole other story.
I'll wait for the copy of Machinery's Thread Book (ordered last night) and see if I can beat the OP's engineer to come up with a name for this thread. Whether a tap for it will available is a whole other story.
anoccasionalyachtsman
Well-Known Member
Thinking a bit further.
I'd be quite surprised if the actuator rod is steel, and that may help explain why its thread has been sufficiently damaged by the Alu alloy extension piece. (Surprised because of its propensity for corrosion, magnetic properties and the fact that my old A/H was Alu alloy).
This may mean that tapping the existing hole to correct the galling damage may not leave enough meat. First thing I'd try is to see if I could clear enough of the mess with a thin chisel to let me reassemble it with a filler of epoxy. I was going to say drill and pin it too, but Vic's point on wall thickness probably negates that.
Failing that rather than scrap the thing I'd consider cutting off the damaged end and permanently attaching the extension. This is where the BSP option might be simpler.
I'd be quite surprised if the actuator rod is steel, and that may help explain why its thread has been sufficiently damaged by the Alu alloy extension piece. (Surprised because of its propensity for corrosion, magnetic properties and the fact that my old A/H was Alu alloy).
This may mean that tapping the existing hole to correct the galling damage may not leave enough meat. First thing I'd try is to see if I could clear enough of the mess with a thin chisel to let me reassemble it with a filler of epoxy. I was going to say drill and pin it too, but Vic's point on wall thickness probably negates that.
Failing that rather than scrap the thing I'd consider cutting off the damaged end and permanently attaching the extension. This is where the BSP option might be simpler.
VicS
Well-Known Member
The push rod of my AH 1000 is almost certainly stainless steel .. and the extension an aluminium alloy.
If i was the OP I think 'd fit a new short extension in with some JB Weld or a similar filled epoxy. Drilling and pinning may be possible too. The bore may be just a bit too large for a 3/8 bsp thread ... perhaps why its the non standard size it is.
winsbury
Well-Known Member
Gentlemen ( and ladies ,)
I am delighted to tell you that the thread has at last been positively identified with the help of Tracy Tools ( I have no connection with them except as a customer .) I sent a pushrod and tip to them and they confirm the size is 11/16 18tpi right hand UNS. Yes, I was surprised it wasn't 19tpi too, it just goes to prove that measuring is very difficult on such a short sample thread length.
Sadly taps and dies for this size are hard to come by and not cheap ( about £150 per 3 x tap & 1 x die set in HSS ) so it's probably not practical to make one's own extensions cost effectively but it might be nice to make a bespoke length one if appearances matter or a number of costly standard extensions are otherwise needed.
To answer some of the other questions, Autohelm 800 and raymarine ST1000 has an anodised tubular aluminium shaft and the ST2000 is stainless, extensions are ( afaik ) all solid aluminium.
I am delighted to tell you that the thread has at last been positively identified with the help of Tracy Tools ( I have no connection with them except as a customer .) I sent a pushrod and tip to them and they confirm the size is 11/16 18tpi right hand UNS. Yes, I was surprised it wasn't 19tpi too, it just goes to prove that measuring is very difficult on such a short sample thread length.
Sadly taps and dies for this size are hard to come by and not cheap ( about £150 per 3 x tap & 1 x die set in HSS ) so it's probably not practical to make one's own extensions cost effectively but it might be nice to make a bespoke length one if appearances matter or a number of costly standard extensions are otherwise needed.
To answer some of the other questions, Autohelm 800 and raymarine ST1000 has an anodised tubular aluminium shaft and the ST2000 is stainless, extensions are ( afaik ) all solid aluminium.
earlybird
Well-Known Member
Strange. Machinery's Handbook lists 6 different recognised UN threads at 11/16" dia. Namely 12, 16, 20, 24, 28 and 32 tpi. None of those are termed UNS although UNS sizes are listed for 5/8" and 3/4" dias. (Presumably means "special").
I'd thought about 20 tpi earlier.
I wonder why one of these wasn't suited to Raymarine's need, seems very fussy.
I'd thought about 20 tpi earlier.
I wonder why one of these wasn't suited to Raymarine's need, seems very fussy.
doug748
Well-Known Member
Good work.
This is the best place I have found for chapter and verse on thread forms:
http://www.ring-plug-thread-gages.com/ti-UN-vs-UNC-vs-UNF-vs-UNEF-vs-UNS.htm
Note, for UNS is recommends:
" Whenever possible, do not design using a UNS special series thread. Stay with the Coarse, Fine, and Extra Fine series in new designs."
No doubt they have used UNS for "commercial" reasons
winsbury
Well-Known Member
Good work.
This is the best place I have found for chapter and verse on thread forms:
http://www.ring-plug-thread-gages.com/ti-UN-vs-UNC-vs-UNF-vs-UNEF-vs-UNS.htm
Note, for UNS is recommends:
" Whenever possible, do not design using a UNS special series thread. Stay with the Coarse, Fine, and Extra Fine series in new designs."
No doubt they have used UNS for "commercial" reasons
Nice link, lots of useful data there. I am sure they did indeed use UNS to keep it almost proprietary.
winsbury
Well-Known Member
oops, made a small error = ST1000 may not be aluminium but the Autohelm 1000 certainly is, which is what I had meant to say.
anoccasionalyachtsman
Well-Known Member
I'm really sorry, but I have an 18tpi thread gauge, and it doesn't fit - could be a dodgy gauge, but my Simrad extension, which is definitely 3/8 BSPP (and so 19tpi) fits the Autohelm thread pitch perfectly.
