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Sine Bar

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Sine Bar

Postby Steve Maskery » 21 Jun 2022, 03:32

Happy 3:30am everyone :(

I need to mark out some compound angles for my dining chairs, so I've made a Sine Bar to get them both accurate and precise. I'll do a proper write-up in due course, but right now I want to go back to sleep. Fat chance, I reckon :(

https://youtu.be/M5n6lXU2d_8

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Re: Sine Bar

Postby novocaine » 21 Jun 2022, 07:07

a wooden sine bar, that's an interesting idea Steve.
I'll shall add it to my watch list.

hope you got some sleep, if not, hope you used the time well. :lol:
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Re: Sine Bar

Postby clogs » 21 Jun 2022, 07:09

sleep, whats that.....?
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Re: Sine Bar

Postby Mike G » 21 Jun 2022, 07:52

"Digital vernier".... :o :shock: ;)

Well, that's a nice little bit of kit, Steve, but I never have the need for accurate angles. I'm sure others will find it useful.
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Re: Sine Bar

Postby Cabinetman » 21 Jun 2022, 08:52

Crikey Steve, that’s some accuracy- to a 10th of an degree, interesting bit of kit which I hadn’t come across before. My iPhone measures to one degree but just how accurate it is I don’t know, if it is accurate I suppose I could use it to show me the full degrees and then subdivide it from there. Ian
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Re: Sine Bar

Postby Andyp » 21 Jun 2022, 08:52

No surprise for most here that I was one of those at the back carving my name in the desk. I’d never heard of a sine bar but enjoyed you vid and explanation. I've never had the need for one either but then that was the case with your square of Thales until I watched your vid.

Thanks Steve.
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cheers
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Re: Sine Bar

Postby Woodster » 21 Jun 2022, 09:20

I’ve got a small sine bar I have used but mostly I use a digital angle gauge. I might have used the sine bar a bit more but you ideally need a gauge block set and I don’t have one.
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Re: Sine Bar

Postby Woodbloke » 21 Jun 2022, 09:21

Mike G wrote:"Digital vernier".... :o :shock: ;)



That's the option I would have gone for. I needed to produce some very accurate chiseling blocks a while back to make a small Japanese kumiko screen to fit in a door. A digital protractor was perfect for the job - Rob
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Re: Sine Bar

Postby Dr.Al » 21 Jun 2022, 09:36

Mike G wrote:"Digital vernier".... :o :shock: ;)


In the defence of "digital vernier" as an expression, some digital callipers use two capacitative sensing tracks in a Vernier arrangement (to give an absolute measurement rather than incrementally tracking movement), so while the visible scale isn't a Vernier one (it's an LCD), the internal scale might still be. "Digital calliper" is probably still a better name, but "digital vernier" might not actually be wrong.
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Re: Sine Bar

Postby Steve Maskery » 21 Jun 2022, 10:10

Hey, I've been out-pedanted! That doesn't happen very often.
Fantastic! :)
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Re: Sine Bar

Postby Eric the Viking » 21 Jun 2022, 20:31

I've had terrible luck with "digital" angle gauges:

My "gem [insert colour here]" box is far from a gem. It's basically a pendulum arrangement and gets stuck near horizontal (just where you need it to zero and stay there!). The case also doesn't have parallel sides (section of a square pyramid), so you never quite know - untrustworthy in summary.

The first digital angle gauge I bought had a cumulative error. If you zeroed the arms at 180 deg. (i.e. using a straightedge or a ruler), it was way off at 90 degrees - possibly 0.5 deg. This was because the internal scale was not mounted in the middle of the disc, but was like an old-style LP with an off-centre hole in it. I don't think they are checked for accuracy in manufacture.

I've also had two linear digital gauges go faulty ("verniers"). one of which arbitrarily just stopped counting around the 3" mark. In contrast, the newest I-Gauging one, which a good friend gave me for Christmas (mm and inches+fractions) is excellent and is great to use.

I do occasionally need quite accurate angles in the workshop, and I think Steve's idea to make a sine bar in wood is a really good one. I only usually use my digital angle gauge as an upmarket sliding bevel, for transferring angles, with the added disadvantage that you can only get an internal angle from it, unlike an actual sliding bevel.

So I'll be making a "Maskery" sine bar at the first opportunity!

E.
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Re: Sine Bar

Postby Mike G » 21 Jun 2022, 20:44

Woodbloke wrote:
Mike G wrote:"Digital vernier".... :o :shock: ;)



That's the option I would have gone for. I needed to produce some very accurate chiseling blocks a while back to make a small Japanese kumiko screen to fit in a door. A digital protractor was perfect for the job - Rob


I think you may have missed my point, Rob.
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Re: Sine Bar

Postby Woodbloke » 22 Jun 2022, 07:21

Mike G wrote:
Woodbloke wrote:
Mike G wrote:"Digital vernier".... :o :shock: ;)



That's the option I would have gone for. I needed to produce some very accurate chiseling blocks a while back to make a small Japanese kumiko screen to fit in a door. A digital protractor was perfect for the job - Rob


I think you may have missed my point, Rob.

Probably did; wouldn't be the first time (or last) :lol: - Rob
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Re: Sine Bar

Postby Raymedullary » 22 Jun 2022, 09:30

I use an engineering sine bar quite often. Last time was to make a block to set my mitre trimmer up :D Its spot on.
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Re: Sine Bar

Postby Peri » 24 Jun 2022, 17:51

We get our students to make a metal sine bar in their milling class.

Steve Maskery wrote:........get them both accurate and precise.


I made the mistake of using that phrase to my engineering mentor. He said "Can you please explain the difference between accuracy and precision?"

I had to go away and fire up google - it was a much harder task than I anticipated. :lol: :lol:
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Re: Sine Bar

Postby novocaine » 24 Jun 2022, 18:41

Peri wrote:We get our students to make a metal sine bar in their milling class.

Steve Maskery wrote:........get them both accurate and precise.


I made the mistake of using that phrase to my engineering mentor. He said "Can you please explain the difference between accuracy and precision?"


I had to go away and fire up google - it was a much harder task than I anticipated. :lol: :lol:


Repeatable vs hitting the mark.
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Re: Sine Bar

Postby Steve Maskery » 24 Jun 2022, 20:20

I would characterise the difference between saying that at my workshop is 8 m long, which is quite accurate, but not very precise, vs saying that my workshop is is 7.937 m long, which is very precise but not necessarily very accurate.
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Re: Sine Bar

Postby Peri » 24 Jun 2022, 20:29

His explanation - that he told to a group of students at the same time - involved a hypothetical dartboard and 9 darts.

I can't remember exactly, something along the lines of "I'm aiming for treble top. One group of 9 darts is tightly clustered around double 14, the other set is scattered about the board, with 2 actually hitting treble top. Which set is precise, and which set is accurate?"

I may have totally mangled that thought exercise, but it's an image that's stayed over the years :D
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Re: Sine Bar

Postby Phil Pascoe » 24 Jun 2022, 20:31

Quite accurate? Almost exactly, nearly.
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Re: Sine Bar

Postby RogerS » 24 Jun 2022, 21:44

Peri wrote:.... He said "Can you please explain the difference between accuracy and precision?"

.....:


They are both religious terms.

'Accuracy' is Roman Catholic whereas 'precision' is Hebrew :D
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Re: Sine Bar

Postby RogerS » 24 Jun 2022, 21:46

Phil Pascoe wrote:Quite accurate? Almost exactly, nearly.


I was wandering through Hexham market the other day and there was a stall selling old and not so old tools. I drooled over this beautifully made vertical height measuring precision instrument from Poland. I nearly bought it...it just ooozed quality. Would not have had the faintest idea how to use it ...
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Re: Sine Bar

Postby novocaine » 24 Jun 2022, 23:08

RogerS wrote:
Phil Pascoe wrote:Quite accurate? Almost exactly, nearly.


I was wandering through Hexham market the other day and there was a stall selling old and not so old tools. I drooled over this beautifully made vertical height measuring precision instrument from Poland. I nearly bought it...it just ooozed quality. Would not have had the faintest idea how to use it ...


I have a height gauge from Moore and Wright, i own it from anothwr life . One of those tools, when you need it, nothing beats it, otherwise it looks good on the shelf behind in zoom meetings.
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