Slimy38
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| posted on 27/9/22 at 07:56 PM |
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How straight is RHS?
Bear with me, this might be a little of an odd question. I have a guitar that needs a bit of maintenance. In particular it needs the frets levelling.
A levelling beam isn't an expensive tool, basically some sandpaper stuck to a very flat bar.
But I was thinking, I have a garage full of bar, and a stack of sandpaper. Could I do a locost option with a length of metal?
My first thought was a spirit level, but I rapidly figured out that none of my levels have got a flat surface. I'm guessing it's partly the
paint or protective coating, hence me coming back to bare metal.
Given that I want about 18 inches of levelling beam, what level of flatness could I expect from stock RHS, for example the 2mm thick 25mm square
section that I used? If I cut off a section then compared it against another length but on each combination of four sides, would that show a good
level of flatness?
[Edited on 27/9/22 by Slimy38]
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pewe
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| posted on 27/9/22 at 09:15 PM |
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I guess the best way to determine that is to use a known straight edge and a set of feeler guages.
Alternatively go buy a sheet of plate glass from a glazier supplier as that's pretty flat.
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Mr Whippy
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| posted on 28/9/22 at 06:43 AM |
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You have to weigh the cost of a proper tool against the cost of repairs once you've screwed up your guitar. As RHS has not been manufactured to
be exactly flat I would not expect it to be close enough without further work, you could try lapping one piece against another with some abrasive and
averaging out the surface but there's no guarantee. Also plate glass isn't flat, it's smooth. Glass is actually quite flexible and will
just conform to the surface beneath it. How about asking around some local guitar clubs/groups to see if someone can do it for you?
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coyoteboy
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| posted on 28/9/22 at 07:59 AM |
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One of those situations where I would think "I could do this the cheap way, but the tool is cheap so I'll do it properly"
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loggyboy
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| posted on 28/9/22 at 08:56 AM |
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If a spirit level isn't flat/smooth enough then I cant see that any 'normal' flat surface will be close enough either.
Mistral Motorsport
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nick205
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| posted on 28/9/22 at 09:05 AM |
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I'm not a guitar player, but from experience with RHS and other steel stock I do know that's not particularly flat. As commented above,
it's not really made to be.
I'd buy the correct tool for the job or perhaps investigate tool hire options (I hired a 1/2" router for fitting kitchen my worktop, far
cheaper than buying one).
Again not playing the guitar or being in the musical instrument world, can you get the job done by a guitar shop/builder? Might be a cost effective
route to a decent result with some back up should there be an issue.
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nick205
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| posted on 28/9/22 at 09:12 AM |
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One further thought...
Some years back I worked in a CNC machine shop. The inspection dept. had a flat surface that was a great big marble appearance block about 500mm x
500mm (2 man job to lift/move it). I doubt they'd have wanted sand paper grit in there, but there are places that have properly flat surfaces.
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coyoteboy
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| posted on 28/9/22 at 09:28 AM |
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quote:
Originally posted by nick205
One further thought...
Some years back I worked in a CNC machine shop. The inspection dept. had a flat surface that was a great big marble appearance block about 500mm x
500mm (2 man job to lift/move it). I doubt they'd have wanted sand paper grit in there, but there are places that have properly flat surfaces.
FWIW I needed a "known flat" surface for some small parts inspection and while we waited for the larger inspection table (as you say,
500x500x200 granite) I bought an IKEA granite chopping board (much like this argos one https://www.argos.co.uk/product/7662403?clickPR=plp:1:2) and
took it to the local machine shop, who confirmed it was +/- 0.03mm across its surface. 30 microns ain't bad for a home use flat surface!
[Edited on 28/9/22 by coyoteboy]
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nick205
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| posted on 28/9/22 at 09:41 AM |
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quote:
Originally posted by coyoteboy
quote:
Originally posted by nick205
One further thought...
Some years back I worked in a CNC machine shop. The inspection dept. had a flat surface that was a great big marble appearance block about 500mm x
500mm (2 man job to lift/move it). I doubt they'd have wanted sand paper grit in there, but there are places that have properly flat surfaces.
FWIW I needed a "known flat" surface for some small parts inspection and while we waited for the larger inspection table (as you say,
500x500x200 granite) I bought an IKEA granite chopping board (much like this argos one https://www.argos.co.uk/product/7662403?clickPR=plp:1:2) and
took it to the local machine shop, who confirmed it was +/- 0.03mm across its surface. 30 microns ain't bad for a home use flat surface!
[Edited on 28/9/22 by coyoteboy]
Good call - IKEA's usually pretty inexpensive too. Personally I'm devoutly anti-IKEA, because SWMBO always ends up buy too much in there.
If you can go alone and simply swoop in/out for that single item your on a winner 
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Slimy38
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| posted on 28/9/22 at 11:37 AM |
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Ah, good call re the granite board, I was actually thinking about something like that for other 'flatness' tasks. I did have a look at
random sheets of glass last night (IE our windows!) and it was very clear that none of them are even close to flat!
The ideal solution would be a guitar shop or luthier to get it set up, but I'm more interested in the process rather than just getting the job
done. I think I'll go for the proper tool though, and a quick shopping trip to Ikea... 
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pigeondave
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| posted on 28/9/22 at 12:30 PM |
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Straightness:
Max 0.2% of total length & 3mm over every 1m length. but thats for Celsius 355
Bluebook says
https://www.steelforlifebluebook.co.uk/tolerances/ec3-ukna/hfshs-hfrhs/
Tata blue book give a little tighter
https://www.tatasteelbluebook.com/en-gb/building-codes/bs-5950/tolerances/cold-formed-shs-and-rhs/
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David Jenkins
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| posted on 28/9/22 at 09:14 PM |
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Whatever the specification says - once it gets to the steel stockist it will be put on a rack where the whole length may only be supported in 3 or 4
places, so if you get a piece from the bottom of the pile is will NOT be straight!
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nick205
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| posted on 29/9/22 at 07:54 AM |
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quote:
Originally posted by David Jenkins
Whatever the specification says - once it gets to the steel stockist it will be put on a rack where the whole length may only be supported in 3 or 4
places, so if you get a piece from the bottom of the pile is will NOT be straight!
Spot on!
1. It will also have been bashed about
2. The ends will need cutting square
3. It'll have dents along it's length
4. There's a fair chance it may be squashed so it's no longer particularly accurate to it's original profile
From experience steel stockholders aren't gentle people and often move the stuff with forlifts, pallet trucks, their boots etc.
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coyoteboy
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| posted on 29/9/22 at 08:12 AM |
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quote:
Originally posted by nick205
quote:
Originally posted by David Jenkins
Whatever the specification says - once it gets to the steel stockist it will be put on a rack where the whole length may only be supported in 3 or 4
places, so if you get a piece from the bottom of the pile is will NOT be straight!
Spot on!
1. It will also have been bashed about
2. The ends will need cutting square
3. It'll have dents along it's length
4. There's a fair chance it may be squashed so it's no longer particularly accurate to it's original profile
From experience steel stockholders aren't gentle people and often move the stuff with forlifts, pallet trucks, their boots etc.
Yep, unless you're a big business and doing incoming inspections, you get what you get.
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jps
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| posted on 29/9/22 at 11:03 AM |
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quote:
Originally posted by Slimy38
I'm more interested in the process rather than just getting the job done.
This question probably renders my question moot, presumably it's not wildly valuable/rare etc! But out of interest - what guitar is it?
Also - this was a revelation for me when I saw it (having recently re-started playing guitar/bought one, after a break of about 20 years):
https://www.peachguitars.com/plek-your-guitar.htm
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indykid
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| posted on 30/9/22 at 11:35 AM |
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buying a length of 12mm or thicker gauge plate or aluminum tooling plate might be a better option if you really desperately want to DIY but
you'll probably be approaching the cost of the tool for the job (which looks like a length of aluminium extrusion in most cases from what
I've seen)
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Neville Jones
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| posted on 9/10/22 at 08:35 PM |
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I make carbon fibre guitars on occasion.
Procedure with frets is to install them rough but use a good press with jaws same round as the top of the fret board.
To level the frets, get a good flat mill file, and lightly run it along the frets. after marking the top of the frets with a marker pen.
draw the file over the frets, check where marker is taken off.
Repeat above, but with opposite side of file.
If the file is flat, marker will be removed same both sides.
Most flat mill files are flat and straight enough for the job, but I usually buy three, and one will be the best.
After the file, use a fret profile file to get the rounded top again.
Tools from STEWMAC. You'll get everything you need from Stewmac.
[Edited on 9/10/22 by Neville Jones]
[Edited on 9/10/22 by Neville Jones]
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Slimy38
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| posted on 10/10/22 at 11:04 AM |
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quote:
Originally posted by jps
quote:
Originally posted by Slimy38
I'm more interested in the process rather than just getting the job done.
This question probably renders my question moot, presumably it's not wildly valuable/rare etc! But out of interest - what guitar is it?
Also - this was a revelation for me when I saw it (having recently re-started playing guitar/bought one, after a break of about 20 years):
https://www.peachguitars.com/plek-your-guitar.htm
It's a Harley Benton, one of these;
https://www.thomann.de/gb/harley_benton_st_20hss_sbk_standard_series.htm
As you can see, not exactly breaking the bank!! It plays nice though, I like the sound and compared to the acoustic that we bought my son a while
back, it actually stays in tune for more than five minutes.
I think running this guitar through that sort of machine would be huge overkill though, and probably cost more than the guitar is!
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