Hi All,

I have one of those TFT arm mounts (BT7513) that I want to use for my
daughters 19" screen.

The mount is adjustable in most planes except the vertical and we
aren't sure exactly where she will have the screen as yet so I wanted
to provide some flexibility there.

Her room was lined with a soft fibre-board (to provide a bit of
insulation and be drawing pin friendly) so that's not very good for
attaching things.

My BIL has some offcuts of Trespa and I fancied attaching a (say)
100mm wide by 500mm high strip of it to the bit of wall above her
worktop, under her (fitted in the ceiling) bed and on top of the fibre
board (I should be able to get a couple of Fischer plugs in there (top
.. middle).

Then, (pre fitting) I fancied drilling / tapping (6 or 8mm d) a row of
suitably spaced holes up the vertical of this 'backing plate' so that
we could adjust the height of the BT7513 easily? The arm mount has 3
holes (and I would use them all) so only the top and middle would be
doing any real 'work'.

So, would anyone know if 18mm of Trespa would tap ok and then how
strong would that tapping be please?

Oh and she's into Rock so wouldn't want to paint it pink or anything
and in fact would probably like the 'industrial' look ;-)

All the best ..

T i m

We use Trespa benching at work, and it is (a) very heavy and (b) very
strong. I once had to put a 22mm hole through a piece, and even with a
sharp bit, the battery on my cordless drill was flagging by the time I
achieved full penetration......
I reckon it should be fine for what you propose, though I would
recommend a coarse threadform, anyone for Whitworth??

PTE

On 8 Feb 2006 06:21:19 -0800, wrote:

We use Trespa benching at work, and it is (a) very heavy and (b) very
strong. I once had to put a 22mm hole through a piece, and even with a
sharp bit, the battery on my cordless drill was flagging by the time I
achieved full penetration......

I bet ;-(

I reckon it should be fine for what you propose, though I would
recommend a coarse threadform, anyone for Whitworth??

Hmm , I know I have a fairly good range of Whitworth taps in the
workshop but can you still get Whitworth machine screws!

Maybe I'll have to buy an old Brit motorbike and nick some of the
bolts off that ;-)

All the best ..

T i m

On Wed, 08 Feb 2006 12:03:02 GMT, T i m wrote:

So, would anyone know if 18mm of Trespa would tap ok and then how
strong would that tapping be please?

Whitworth, UNC, or the coarse series metric threads are fine. Polyester
resin glued-in rock anchors work too.

Thread inserts won't work, as the coarse "wood thread" side of them just
isn't strong enough to tap the Trespa.

On Wed, 08 Feb 2006 20:49:11 +0000, Andy Dingley
wrote:

On Wed, 08 Feb 2006 12:03:02 GMT, T i m wrote:

So, would anyone know if 18mm of Trespa would tap ok and then how
strong would that tapping be please?

Whitworth, UNC, or the coarse series metric threads are fine. Polyester
resin glued-in rock anchors work too.

Do they do a 'coarse' pitch metric in 6mm do you know Andy (is 'std'
1.25)?

Thread inserts won't work, as the coarse "wood thread" side of them just
isn't strong enough to tap the Trespa.

Ok .. thanks ;-)

All the best ..

T i m

T i m wrote:
Hi All,

I have one of those TFT arm mounts (BT7513) that I want to use for my
daughters 19" screen.

The mount is adjustable in most planes except the vertical and we
aren't sure exactly where she will have the screen as yet so I wanted
to provide some flexibility there.

Her room was lined with a soft fibre-board (to provide a bit of
insulation and be drawing pin friendly) so that's not very good for
attaching things.

My BIL has some offcuts of Trespa and I fancied attaching a (say)
100mm wide by 500mm high strip of it to the bit of wall above her
worktop, under her (fitted in the ceiling) bed and on top of the fibre
board (I should be able to get a couple of Fischer plugs in there (top
. middle).

Then, (pre fitting) I fancied drilling / tapping (6 or 8mm d) a row of
suitably spaced holes up the vertical of this 'backing plate' so that
we could adjust the height of the BT7513 easily? The arm mount has 3
holes (and I would use them all) so only the top and middle would be
doing any real 'work'.

So, would anyone know if 18mm of Trespa would tap ok and then how
strong would that tapping be please?

Oh and she's into Rock so wouldn't want to paint it pink or anything
and in fact would probably like the 'industrial' look ;-)

All the best ..

T i m

even after looking at the site Im not much wiser as to what it is, or
what it costs. Sounds like it just might be what I've been looking for
for the bathroom.

NT

On 8 Feb 2006 13:53:37 -0800, wrote:


So, would anyone know if 18mm of Trespa would tap ok and then how
strong would that tapping be please?

Oh and she's into Rock so wouldn't want to paint it pink or anything
and in fact would probably like the 'industrial' look ;-)

All the best ..

T i m

even after looking at the site Im not much wiser as to what it is

An acid resistant, very dense composite material used typically in lab
worktops / upstands (instead of the *more* expensive / fragile
marble).

, or
what it costs.

A lot ;-)

Sounds like it just might be what I've been looking for
for the bathroom.

My BIL gave me a bit about 4' long, 4" wide and 5/8" thick today and
when you pick it up it feels like a lump of steel ;-)

Apparently it kills most ordinary tools you try to cut it with (if you
aren't very careful) ;-(

I'll let you know tomorrow ;-)

All the best ..

T i m

On Wed, 08 Feb 2006 21:18:00 GMT, T i m wrote:

Do they do a 'coarse' pitch metric in 6mm do you know Andy (is 'std'
1.25)?

Coarse M6 is 1.0 and fine is 0.75

I'd use M8, which is 1.25 for coarse and 1 or 0.75 for fine.

On 8 Feb 2006 13:53:37 -0800, wrote:

even after looking at the site Im not much wiser as to what it is, or
what it costs. Sounds like it just might be what I've been looking for
for the bathroom.

You can't afford Trespa - no-one can.
But there's always a scrum over the offcuts 8-)

BTW If you dishwash Trespa a few times (I've got kitchen knives handled
with it) the dye washes out of the fabric reinforcement and it develops
a "woodgrain" appearance.

Andy Dingley wrote:
On 8 Feb 2006 13:53:37 -0800, wrote:

even after looking at the site Im not much wiser as to what it is, or
what it costs. Sounds like it just might be what I've been looking for
for the bathroom.

You can't afford Trespa - no-one can.
But there's always a scrum over the offcuts 8-)

BTW If you dishwash Trespa a few times (I've got kitchen knives handled
with it) the dye washes out of the fabric reinforcement and it develops
a "woodgrain" appearance.

ty, just what I wanted to know.


nt

Andy Dingley wrote:

Whitworth, UNC, or the coarse series metric threads are fine. Polyester
resin glued-in rock anchors work too.

Thread inserts won't work, as the coarse "wood thread" side of them just
isn't strong enough to tap the Trespa.

Why not drill through & secure it with nuts & washers on the rear of
the Trespa? Offer up to the fibre board & counter bore the marked
impressions to accomodate the nuts. No taps involved.

On Thu, 09 Feb 2006 01:05:13 +0000, Andy Dingley
wrote:

On Wed, 08 Feb 2006 21:18:00 GMT, T i m wrote:

Do they do a 'coarse' pitch metric in 6mm do you know Andy (is 'std'
1.25)?

Coarse M6 is 1.0 and fine is 0.75

I'd use M8, which is 1.25 for coarse and 1 or 0.75 for fine.

Thanks for that.

The current holes in the bracket wall plate part are only ~6mm dia at
the moment but would easily open up the clear an 8mm machine screw. To
stand a chance of getting the little plastic cover back on I'd either
have to use pan head screws or countersink the holes (one 'hole' is
round and quite deep (two layers of steel) so that would take a
countersunk easily but the top one is 'slotted' (for adjustment of the
vertical alignment) so that might have to be pan (as it only goes
through one layer of steel).


All the best ..

T i m

On 9 Feb 2006 01:59:46 -0800, "Aidan" wrote:


Andy Dingley wrote:

Whitworth, UNC, or the coarse series metric threads are fine. Polyester
resin glued-in rock anchors work too.

Thread inserts won't work, as the coarse "wood thread" side of them just
isn't strong enough to tap the Trespa.

Why not drill through & secure it with nuts & washers on the rear of
the Trespa? Offer up to the fibre board & counter bore the marked
impressions to accomodate the nuts. No taps involved.

Nice idea BUT, the object of this exercise it to provide vertical
'adjustment' for the flat screen and once the trespa is fitted to the
wall I don't intend taking it down again ;-)

I could actually just fit the bracket in position with some turned
nylon spacers to hold the bracket just off the surface of the
fibrerboad 'lining', but if she decides she wants the scanner under
the screen or sumat and therefore the screen needs to 'move up an
inch' I'm stuffed?

With this pre-drilled / tapped idea and the Trespa (only using that
because a) I can get some free, b) I don't need to paint it, c) it's
nice and flat / strong and d) it will (hopefully) take a tapped thread
to allow my incremental hight adjustment idea?

To do the adjustment you lift off the TFT, unclip the bracket cover,
unscrew the two 8 x 1.25 machine screws, select an alternative
position, replace the screws, repace the cover, replace the TFT ;-)

And if this 19" screen dies and we are offered a 21" replacement we
can accommodate that as well (and not only can we adjust to it easily
it won't pull *my* bracket off the wall!) ;-)


I suppose all the above is a function of what I am / how I think .. (I
think I'm a frustrated inventor of sorts g). I don't really care how
long it takes (within reason of course) or how complicated it may seem
to others as long as it's 'right' for me (and there are only a few
rights and hundreds of wrongs). It's also nice to have folk (who
understand these things) see your effors and say 'that's a good idea'
, 'how did you do that?' or 'you've made a nice job of that' blush
;-)

If I do something I would like to think all the options have been
considered, it provides the most practical / flexible solution and I
never have to do it again? If I wanted a quick solution and wasn't
interested in the d-i-y part of it then I'd get someone else in to do
it .. the problem with that is many 'tradesmen' today have little
imagination / engineering skills and I *know* I wouldn't be satisfied
with the job (present company accepted of course!) ;-)

So, "whatever you do do, do do well" ..(unless you are trying to earn
a living out of it 'these days' I suppose ...sigh) ;-(

All the best ..

T i m

On Thu, 09 Feb 2006 01:05:13 +0000, Andy Dingley
wrote:

On Wed, 08 Feb 2006 21:18:00 GMT, T i m wrote:

Do they do a 'coarse' pitch metric in 6mm do you know Andy (is 'std'
1.25)?

Coarse M6 is 1.0 and fine is 0.75

I'd use M8, which is 1.25 for coarse and 1 or 0.75 for fine.

Good job you mentioned that Andy ...

I just checked out the replacement 'Blue Wizard' 8m x 1.25 tap I
bought the other day and noted it was a 9mm ;-(

So I just popped back to the very well equipped tool shop (I leave my
wallet at home and only take the right money with me or I know I'll
spend all of what little I have in there .. I know I will!) and
swapped it for the 8mm .. oh and some quality 14tpi HSS hacksaw blades
... (mumble and a little fold up magnifier, 3 expanding rules (never
find one when you want one) and a 'Mole' style table quick clamp for
the pillar drill doh!).

Then it got me thinking re do I lube or not? For steel and these
forward swarf ejecting 'speed taps' I generally used them in the
DeWalt cordless (on low) and some cutting paste (and then it's a
'knife through butter') ;-)

Apparently if you try cutting Trespa too fast it heats up quickly and
causes all sorts of issues (and the material expands etc). ;-(

I think with some 'plastics' you can lubricate with water?

Maybe I'll just take it slower than usual and see what happens ..

All the best ..

T i m

On Thu, 09 Feb 2006 11:49:02 -0000, T i m wrote:

I just checked out the replacement 'Blue Wizard' 8m x 1.25 tap I
bought the other day and noted it was a 9mm ;-(

Possibly worse than you think. 9mm AFAIK is not part of the ISO standard
series. Some years ago I had to make a replacement part with a 9x1.25
thread and dies were hard to find. I think that after 8M the sizes in the
standard series go up in steps of two. Machine screws and nuts and bolts
in that size may well be as hard to find as rocking horse doo-doo. You may
have to buy a whole box, in which case it may be cheaper buying a new tap.
Good luck in any case.

John Schmitt

--
Using Opera's revolutionary e-mail client: http://www.opera.com/mail/

On Thu, 09 Feb 2006 12:17:57 -0000, "John Schmitt"
wrote:

On Thu, 09 Feb 2006 11:49:02 -0000, T i m wrote:

I just checked out the replacement 'Blue Wizard' 8m x 1.25 tap I
bought the other day and noted it was a 9mm ;-(

Possibly worse than you think.

Go on .. ;-)

9mm AFAIK is not part of the ISO standard
series.

Ooo err .. funny as I was swapping it I was considering keeping it ..
you know .. for the collection but couldn't actually remember ever
seeing a 9mm bolt?

Some years ago I had to make a replacement part with a 9x1.25
thread and dies were hard to find.

Ah .. ;-(

I think that after 8M the sizes in the
standard series go up in steps of two.

That seems to make sense. I'm pretty sure I have a selection of 10m
bolts etc ..

Machine screws and nuts and bolts
in that size may well be as hard to find as rocking horse doo-doo. You may
have to buy a whole box, in which case it may be cheaper buying a new tap.

Swaped already ;-)

Good luck in any case.

Cheers. I don't know if I should drill / tap a test thread first and
see how hard I can tighten it (with a pozi headed screw to be
'realistic') befo

1) I can't tighten it any more ;-)
2) It strips the thread ;-(
3) I shear the screw off! ;-)

The problem with these 'L' shaped arm wall brackets is the top
mounting is screw nearly completely in tension (when the arm is at 90
deg to the bracket), both from the holding force and the load on the
arm?

I'm sure someone here can do the sums for me ..

The TFT weighs 6.5 kg and at full extension is approx 500 mm from the
bracket. Assuming the 160 mm high bracket is completely rigid (which
it isn't I know) and the top fixiing is actually 30 mm from the top
of the plate (therefore and possibly more importantly 130 from the
bottom where I assume it would try to pivot?), what sort of tension
would be in the top fixing please? Would a std grade 8 x 1.25 hold it
;-)

(I guess it should as they provide 3 x No10 x 40mm screws / plugs in
the kit)

(fwiw the arm minus wall bracket weighs another 1.2kg?)

All the best ..

T i m

On Thu, 09 Feb 2006 13:09:59 -0000, T i m wrote:

Cheers. I don't know if I should drill / tap a test thread first and
see how hard I can tighten it (with a pozi headed screw to be
'realistic') befo

1) I can't tighten it any more ;-)
2) It strips the thread ;-(
3) I shear the screw off! ;-)

If the Trespa is as tough as has been mentioned, you will probably find
that the driver bit will "cam out" before any of those happen to an M8
screw.

The problem with these 'L' shaped arm wall brackets is the top
mounting is screw nearly completely in tension (when the arm is at 90
deg to the bracket), both from the holding force and the load on the
arm?

I'm sure someone here can do the sums for me ..

The TFT weighs 6.5 kg and at full extension is approx 500 mm from the
bracket. Assuming the 160 mm high bracket is completely rigid (which
it isn't I know) and the top fixiing is actually 30 mm from the top
of the plate (therefore and possibly more importantly 130 from the
bottom where I assume it would try to pivot?), what sort of tension
would be in the top fixing please? Would a std grade 8 x 1.25 hold it
;-)

Rule of thumb: 6mm steel rod is good for an ultimate load (i.e. the metal
fails) of approx 1 ton(nne). 8mm 1 3/4, 10mm 2 3/4. Exactly how much
overkill are you after? ;-)

http://catalog.thecrosbygroup.com/BODY_138.HTM

suggests that I an being conservative on the larger diameters. If you fix
it to the wall and then do can a pullup on it without it failing, this
would suggest a factor of safety in the region of 10 or greater.

(I guess it should as they provide 3 x No10 x 40mm screws / plugs in
the kit)

In direct tension and well installed that combination should be good for
at least 150 kg in direct tension, probably rather more. Dont forget that
most telly brackets are designed for something like 21" tubed TVs which
come in at about 25kg, with the weight concentrated towards the front.

(fwiw the arm minus wall bracket weighs another 1.2kg?)

John Schmitt

--
Using Opera's revolutionary e-mail client: http://www.opera.com/mail/

On Thu, 09 Feb 2006 14:34:44 -0000, "John Schmitt"
wrote:

On Thu, 09 Feb 2006 13:09:59 -0000, T i m wrote:

Cheers. I don't know if I should drill / tap a test thread first and
see how hard I can tighten it (with a pozi headed screw to be
'realistic') befo

1) I can't tighten it any more ;-)
2) It strips the thread ;-(
3) I shear the screw off! ;-)

If the Trespa is as tough as has been mentioned, you will probably find
that the driver bit will "cam out" before any of those happen to an M8
screw.

That would be my wrist discolating then (some of us still like the
feel of a screwdriver for some jobs) ;-)

The problem with these 'L' shaped arm wall brackets is the top
mounting is screw nearly completely in tension (when the arm is at 90
deg to the bracket), both from the holding force and the load on the
arm?

I'm sure someone here can do the sums for me ..

The TFT weighs 6.5 kg and at full extension is approx 500 mm from the
bracket. Assuming the 160 mm high bracket is completely rigid (which
it isn't I know) and the top fixiing is actually 30 mm from the top
of the plate (therefore and possibly more importantly 130 from the
bottom where I assume it would try to pivot?), what sort of tension
would be in the top fixing please? Would a std grade 8 x 1.25 hold it
;-)

Rule of thumb: 6mm steel rod is good for an ultimate load (i.e. the metal
fails) of approx 1 ton(nne). 8mm 1 3/4, 10mm 2 3/4. Exactly how much
overkill are you after? ;-)

;-)

http://catalog.thecrosbygroup.com/BODY_138.HTM

suggests that I an being conservative on the larger diameters.

But (and brings us back to the op) I felt there was more chance of the
thread ripping out of the Trespa than the steel screw failing (as
strong as Trespa *might* be)? But like balsa wood, it's very strong
for it's weight but not *strong* in the traditional sense of the word?

If you fix
it to the wall and then do can a pullup on it without it failing, this
would suggest a factor of safety in the region of 10 or greater.

And how I often test such things but this will end up under a raised
bed and over a worktop ;-)

(I guess it should as they provide 3 x No10 x 40mm screws / plugs in
the kit)

In direct tension and well installed that combination should be good for
at least 150 kg in direct tension, probably rather more.

Ok ..

Dont forget that
most telly brackets are designed for something like 21" tubed TVs which
come in at about 25kg, with the weight concentrated towards the front.

Indeed .. and most of the telly brackets I have used have a distinct
inverted 'channel' section to the wall mouting plate to spread the
load from the fastenings over the base. *This* wall mounting bracket
is only 3mm thick steel (with some 'hinges' welded through (rather
than 'to' making the hinges stronger but the plate weaker)) suggesting
a much lower expected load (than a telly) ;-)

As mentioned the TFT is 6.5kg, the arm another 1.2 (so worst case
7.7kg) and the bracket (and presumably supplied fastenings) is
supposed to be good for 15kg (with some in reserve no doubt).

However I'm not sure I'd trust the fastenings given even if I was
going to mount the thing directly to the wall of this 1897 house
(where most of the mortar is now sand!) ;-)

I think I'll start with my design and simply test how well one screw
bits down and use that to predict how well it will all hold up in the
real world (assuming the thread taps out ok I'm sure it will be fine)
;-)

All the best ..

T i m

On Thu, 09 Feb 2006 15:37:57 -0000, T i m wrote:

But (and brings us back to the op) I felt there was more chance of the
thread ripping out of the Trespa than the steel screw failing (as
strong as Trespa *might* be)? But like balsa wood, it's very strong
for it's weight but not *strong* in the traditional sense of the word?

A little bit of web browsing suggests that trespa is about 1/5 the tensile
strength of mild steel, suggesting that a single 6mm threaded fastening
will pull out in the near neighborhood of 100 kgf, 8mm 150 kgf. Creep is
the next consideration.

John Schmitt


--
Using Opera's revolutionary e-mail client: http://www.opera.com/mail/

On Thu, 09 Feb 2006 12:17:57 -0000, "John Schmitt"
wrote:

Possibly worse than you think. 9mm AFAIK is not part of the ISO standard
series.

It's part of the series (ie. they define the thread form and pitch) but
it's one of the "second choice" size recommendations so it's not widely
used.

Volvo probably use it. I've never known a car with so many of those odd
"even" metric spanners needed. I've had to use spanners from sets I've
owned for 20 years and never used.

T i m wrote:

I'm sure someone here can do the sums for me ..

The TFT weighs 6.5 kg and at full extension is approx 500 mm from the
bracket. Assuming the 160 mm high bracket is completely rigid (which
it isn't I know) and the top fixiing is actually 30 mm from the top
of the plate (therefore and possibly more importantly 130 from the
bottom where I assume it would try to pivot?), what sort of tension
would be in the top fixing please? Would a std grade 8 x 1.25 hold it
;-)

Sounds like the arm has just under a 5:1 mechanical advantage over the
bracket at full extension. The weight of the monitor plus arm is
probably only a proportion of the total typical load since manhandling
the monitor to reposition it will increase the potential load a bit.

So say you allow 12kg worst case, that would give you 60kg (or 600N)
pull on the top fixings.

(I guess it should as they provide 3 x No10 x 40mm screws / plugs in
the kit)

Which sounds like it ought to be more than adequate for a wall fixing.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Mon, 13 Feb 2006 12:14:40 +0000, John Rumm
wrote:

T i m wrote:

I'm sure someone here can do the sums for me ..

The TFT weighs 6.5 kg and at full extension is approx 500 mm from the
bracket. Assuming the 160 mm high bracket is completely rigid (which
it isn't I know) and the top fixiing is actually 30 mm from the top
of the plate (therefore and possibly more importantly 130 from the
bottom where I assume it would try to pivot?), what sort of tension
would be in the top fixing please? Would a std grade 8 x 1.25 hold it
;-)

Sounds like the arm has just under a 5:1 mechanical advantage over the
bracket at full extension. The weight of the monitor plus arm is
probably only a proportion of the total typical load since manhandling
the monitor to reposition it will increase the potential load a bit.

So say you allow 12kg worst case, that would give you 60kg (or 600N)
pull on the top fixings.

(I guess it should as they provide 3 x No10 x 40mm screws / plugs in
the kit)

Which sounds like it ought to be more than adequate for a wall fixing.

Kewl, thanks for that ;-)

I carried on as planned with the length of Trespa.

First I cut it to length by hand with a new 14tpi HSS blade in the
hacksaw and it cut easily.

I then ran a small rebate off it using the scroll saw with depth stop
and a guide clamped to the job.

I then pilot driled some 27 holes in the pillar drill and that was
probably the most difficult job due to the bit heating in the material
(no matter how fast / slow I worked or set the drill speed).

I then opened the holes out (tapping size) for an 8 x 1.25 mm thread
(an easier job).

I then tapped by hand the 24 'adjustment' holes using a new spiral
nosees speed tap (fairly easy work).

I then adjusted the wall bracket to take the 8mm machine screws and
filed the holes out to pickup the 40mm hole centres (offering 20mm
hight adjustment steps from max to min).

The plate was offered to the wall and drilled though the fixing holes
with a 'pilot' maisonary drill in the DeWalt.

I then removed the plate and drilled the 3 fixing holes (two at the
top and one at the bottom) to take 10mm x 100mm 'Fischer' plugs.

The plate was fitted to the wall and 'nipped up' (so as not to crush
the fibre board room lining).

The bracket and arm attached and 19" TFT positioned.

After collecting the daughter from her b/f's and she saw the bracket I
asked her what she thought ... "Kewl, thanks Dad" .. ;-)

So, quite a bit of effort / tools / thought involved but I'm now
happy that:

1) It isn't going to fall off the wall.
2) I didn't have to paint it.
3) It will be easily adjustable in the future
4) When removed it will only leave 3 x 10mm dia holes.
5) My daughter may see you don't have to use things as it says on the
tin ;-)

All the best to all who offered help / advice ;-)

T i m

"I love it when a plan comes together" ;-)