Sopwith Snipe Project - Page 9

Nick · 31 May 2008, 09:25 PM

Quote:

What have you been told about the accuracy of waterjet cutting?

I keep getting conflicting answers. Laser is definitely accurate enough but the heat is an issue. Some waterjet guys quote me large tolerances like +/-.020" and others say they are as accurate as laser.

Bill,
I hadn't realised there was possibly such a large tolerance issue with Water jet cutting as have not spoken to anyone who's done it. +/- .020" is certainly a bit much. Either way next bunch of fittings I do I will not predrill any holes (apart from the large lightening ones). Even the large lightening holes if close to a bend radius are best cut after bending, as can end up distorting and then just end up in the bin.

Cheers, Nick

brinesharks · 1 June 2008, 12:25 AM

I was intending to use water cutting - I might check up on the accuracy as the guys I have been talking to have done some very fine work.

Would CNC routing/milling work?

brisfitworks · 1 June 2008, 04:27 AM

Silly me!

I sometimes wonder why I talk to people in a field to get information!@#$

I just did what I obviously should have done before - do some literature searching on the "net".

There still seems to be some variations in what answers you get about tolerances. Waterjet machine manufacturer sites claim different tolerances and one with the amazing claim of +/-0.0005" seems to be for a very specific application and a very specific and expensive machine. Probably some salesmanship in the writing versus balancing ones claims.

I found many references to +/-0.005" and references like "80% of waterjet cutters can maintain +/-0.003" accuracy".

I also found reference to taper considerations that must be included in tolerance considerations but this is for materials thicker than we are considering. (that is probably where the fellow with his oversize tolerance statement came from and he was from the laser cutting industry)

It also appears, as would be expected, that there has been a lot of improvements in the technology over the last 5 years! (my last major check into waterjet was a few years ago). Accuracy and cutting speeds have had significant improvements and speed is a big factor for costs! Last time I got stuff quoted at work for waterjetting parts we get laser cut, it wasn't competitive. I think I'll get those requoted.

I found some discussions about machine design improvements that one must watch out for when selecting a machine to purchase and the tolerance difference was +/-.007" for an older style drive technology.

I think that waterjet is still a very good alternative and it looks like improvements in technology and understanding have made it even more viable.

Sorry, should have checked around on the net and updated myself before concerning you all with my post.

brisfitworks · 1 June 2008, 04:37 AM

Nick:

I should have guessed I wasn't the only guy on the planet that went "Oh shit!" when I formed Sopwith spar boxes and had to figure out how to keep those damned lightening holes from distorting their edges!

There is definitely a need to look at a part and decide which holes can be "pre-drilled" (by whatever CNC based flat form cutter we use) and which shouldn't.

The Sopwith spar box is probably the most frustrating and educating part I've had in this process.

I think lightening holes are ok to cut because I think they were likely part of the stamping used in WW1 and thus they had the same issues.

Those bolt holes and Joint Rod holes that pass through the box? Forget it, I filled them with weld to redrill some because of the tolerances and errors in bends.

It really takes some thought and experience to decide which hole to pre-cut or not.

But! I bet if we had the stamping die drawings to know what wasn't "pre-drilled" by Sopwith, we'd have pretty much the same answer. We know the Joint Rod hole is an after forming operation from some of the drawings.

Quote:

Originally Posted by Nick

Bill,
Either way next bunch of fittings I do I will not predrill any holes (apart from the large lightening ones). Even the large lightening holes if close to a bend radius are best cut after bending, as can end up distorting and then just end up in the bin.

Cheers, Nick

Machinbird · 1 June 2008, 07:48 AM

I have a business associate who does waterjet cutting. After posing a few projects to him, it seems that waterjet can cut thicker material than laser and that they often stack cut items. The accuracy is almost the same as laser but has to be specified (do you stack cut or not). Thicker materials do slow the machine down quite a bit and so add machine time costs, but by thicker we are talking 1" plus. Waterjet cutting thicker materials will leave a kerf. Newer waterjets angle the cut forward but this is under software control (corners). Waterjets can cut all sorts of things including paper and fabrics with minimal wetting out of the cutting zone. Key thing about waterjet is no HAZ (heat affected zone). I have thought about getting one but the older intensifier ones are supposed to be extremely noisy and they all suck a lot of power. Accuracy of the waterjet also depends on the condition of the nozzle orifice which degrades over use. Waterjets seem to be a bit of a maintenance hog and are not cheap to purchase.
Since I have not laid my hands on a waterjet unit, anyone with actual experience should feel free to correct my misperceptions.

Joe Perkel · 8 June 2008, 06:12 AM

Nick,

I have tracked down another spectacular period reference.

Aeroplane Structures - Google Book Search

Just ordered a second edition hardcover.

Nick · 8 June 2008, 02:49 PM

Quote:

Originally Posted by Joe Perkel

Nick,

I have tracked down another spectacular period reference.

Aeroplane Structures - Google Book Search

Just ordered a second edition hardcover.

Thanks Joe,
I haven't had any luck with Google Books displaying pages, so have ordered an old copy.

Cheers, Nick

Nick · 9 June 2008, 02:33 AM

On the plans it shows that the spars are laminated from 3 pieces, however on this original photo it would appear to show no lamination but just a solid spar.
Are spars stronger if laminated or not, or was it a matter of producing a spar with the smaller size wood available? Other pictures show the spars to be laminated

Nick

Koloman Mayrhofer · 9 June 2008, 03:04 AM

hallo,
first,exellent work congratulation to your efforts and your decission uppon a lesser known type.

spars are not necessarely stronger if laminated but much more predictable.
especially in all kinds of pine and ash spars we always laminate them. in spruce one can usually get very good quality wood which allow the use of a single piece. but again if you have the slightliest worry about what is inside cut it apart and reglue it. it also allows to use shorter pices of good wood to be scarfjointed and used as laminations. much more economic especially as spruce becomes terrible expensive. one has the idea it is made of oil.

cheers
koloman mayrhofer

Nick · 9 June 2008, 04:25 AM

Quote:

Originally Posted by Koloman Mayrhofer

spars are not necessarely stronger if laminated but much more predictable.
especially in all kinds of pine and ash spars we always laminate them. in spruce one can usually get very good quality wood which allow the use of a single piece. but again if you have the slightliest worry about what is inside cut it apart and reglue it. it also allows to use shorter pices of good wood to be scarfjointed and used as laminations. much more economic especially as spruce becomes terrible expensive. one has the idea it is made of oil.

cheers
koloman mayrhofer

Hi Koloman,
Many thanks for your reply which makes good sense. I have some long lengths of rough sawn spruce which I'll eventually use for the spars. I'll get them cut to the smaller sizes and then reglue them.

Cheers, Nick Caudwell