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Member postings for Dr_GMJN

Here is a list of all the postings Dr_GMJN has made in our forums. Click on a thread name to jump to the thread.

Thread: Measure twice Cut once
22/03/2022 23:09:14
Posted by pgk pgk on 16/03/2022 11:46:40:

Poo happens! It's a question of who gets the blame.

Back in the late 60's my local council of the time built a new set of council offices at a huge cost. They'd got to the second floor when checks revealed that the foundations would be inadequate and the whole thing was knocked down and re-started. A junior was sacked. Who would have thought that a multimillion pound project woudn't have its structural calculations cross-checked? Yeah, likely.

My last year at college and a mate who had graduated and was working as a surveyor on the new Euston railway station told me he discovered a room the length of the mezzanine and a few feet wide with no doors or windows..

pgk

I drove past this place every week, watching it gradually get bigger, then one day it seemed to be getting smaller again…it’s almost finished now:

**LINK**

Thread: Metal Cleaning Using Vinegar?
19/02/2022 20:35:20

Is car alloy wheel cleaner (the stuff in the hand sprayer bottles) based on phosphoric acid? It has a similar smell as rust remover.

Thread: ML7 Bull Wheel Dimensions?
10/02/2022 22:20:08

I printed one yesterday in solid PLA - works fine, apart from It doesn’t fit when the back-gear grease nipple is fitted: It won’t sit low enough to engage with the teeth in order to slide left onto the bull gear.

07/02/2022 18:43:52

Thanks all, I might as well just print the one on thingiverse if it works...I'll find some other Fusion project to do while sitting out self-isolation.

06/02/2022 22:22:34
Posted by David Davies 8 on 06/02/2022 22:21:03:

My ML7 bull wheel is 3.315 inches O/D and has a thickness of 0,625 inches. The gear has 65t and from those figures it must be 20DP. I can't help with the PA but logic says that it would be 14.5 degrees.

HTH

Dave

Thanks very much Dave.

06/02/2022 18:48:09

Does anyone have a drawing of an ML7 Bull wheel and tooth profile?

I want to design and print a lock for chuck removal.

I think there's a free .stl somewhere, but I can't find it, plus I'm stuck in self isolation for 10 days so might as well improve my Fusion 360 skills instead of staring out of the window.

Thanks.

Thread: Hand Held Magnifiers?
06/02/2022 18:41:04
Posted by Nick Clarke 3 on 06/02/2022 09:58:18:

I use an older Eschenbach hand magnifier - 10x magnification and 35mm diameter. Illuminated and the newer versions like the picture below come with a stand. Cromwell sell them for about £45 + VAT and post and Amazon for about £70 presumably all in.

eschenbach.jpg

Thanks Nick - spot-on. Bit more than I wanted to spend, but I'll try and find one.

Thread: Non-warping Wood for Base?
06/02/2022 18:29:29

Thanks all.

Jason - yes, the first option is what I like - I've had no luck with attaching thin veneer to the edges of any veneered MDF furniture I've make, so having the top surface already done is good.

Only difference to what you say is to get overall dims back to 1000 mm x 200 mm, I would have to machine to 988 mm x 198 mm before sticking the 6 mm solid sides and ends onto it.

Another similar option, which would avoid any thin veneer would be to use 6 mm veneered MDF for the top, sides and ends, all cut to be 6 mm short, then glue in square stock and chamfer all edges (top and vertical)? In fact there are lots of combinations of the above. I guess it depends on the capacity of my friend's CNC router becasue I know if I try to do it by hand I won't be happy with it.

06/02/2022 16:08:55
Posted by Clive Hartland on 06/02/2022 15:27:55:

Dr_GMJN.

I am interested which glue you use on the paper models, at the moment I use UHU but get contraction of the joins.

Every other glue has a long drying time. I did try the glue used on balsa models but that also contracts joints, do you have any recomendations?

Clive

Clive,

For large, flat pieces, I use UHU to secure - it doesn't cause wrinkling like PVA because it's not water based - it touches the paper surface and quickly skins over rather than soaking in. This is why I scrapped the first attempt - the PVA soaked into the deck, and gave a horrible egg crate effect where the thin substructure pieces touched it. I've not found it contracts, but wouldn't be surprised. If used as above, contraction shouldn't be an issue anyway.

UHU is useless for small parts because it's stringy and uncontrollable.

For the vast majority of assembly I use Formula 560 PVA canopy glue. I often tape parts together, and paint (sparingly) a slightly thinned bead along the join. Wrinkling isn't much of an issue on corner joints or small parts.

One advantage of Formula 560 is that it's water soluble, so if you screw up you might have a chance of re-dissolving it with water and trying again; it's saved me many times.

Full thread here if you're interested in registering:

Bismarck, HMV, 1:250 - PaperModelers.com

Thanks.

06/02/2022 15:58:23

Sorry Jason, I'm not sure what you mean. After 6 weeks of going stir crazy with a broken foot at Christmas, and now 10 days to self-isolate in the spare bedroom with Covid, I'm not 100% with it.

Do you mean something like this:



I'd have to match the side pieces with the surface somehow, and presumably chamfer the corners? I can't accurately cut wood by hand, so it might be a big ask. A friend has a CNC router he built, so I guess he could do it.

The displays look great by the way. Cheers.

06/02/2022 14:57:57
Posted by Steviegtr on 06/02/2022 00:17:08:

Mainly the most stable of woods is Hardwood. It is expensive, but If you used say solid oak. It would never move. But your bank account would.

Steve.

This is what happened to the solid oak plank I got, after being indoors for a few months:



I can assure you it was a flat as a pancake when I got it.

I realise a lot of factors need to be considered when discussing how prone a certain wood it to warping, and the conditions that might lead to it, but to say solid oak will never move certainly isn't correct.

06/02/2022 14:12:46

Thanks all - That's a nice F-104 Ramon; another prize winner no doubt?

Re oak: I also thought that solid oak would be fine, after all it's a strong, hard wood. It's not the case though. I've got some oak planks in the house left over from some Dinky Toy display cases a friend made for me, and they twist and bow like nothing I've seen.

I definitely want to stick with a wood finish; all my other paper ships are on wooden bases, although they're all different - and importantly much smaller. In hindsight I should have made them all the same style, but these things take a lot of time and I wasn't sure I'd be building more than a couple anyway. They are all 1:250 scale:









They are extremely fragile, and all have perspex cases. I specify the base size of the cases such that the wooden bases fit within them:



The model in question is the Bismarck. As Jason mentioned, a composite shelf is ideal for a temporary base to build on becasue it's dead flat and won't warp. I got one from IKEA which has what looks like a hardboard substructure (possibly with cardboard innards) and laminate surfaces:



You can probably see the relative sizes we're talking about, and the depth of that shelf is 50mm, not the absolute maximum of 30mm I'm after, and is 260mm wide, not the 200mm I want. So it's not a favourable geometry for stiffness. If I could replicate the above at 30mm deep, with a wood finish, and chamfers, I'e be perfectly happy. Doing it is a different matter though. The paper hull structure (floor, bulkheads, stiffeners, decks and sides) have formed a pretty stiff structure. It can easily be picked up at each end and won't deform to any noticeable degree - it's extremely light. However, it would not resist any warping forces at all.

I put the hidden brackets on the office wall, and the model stays there when I'm not working on it. Eventually it will be replaced by a veneered MDF sideboard I'm building (all my other office work surfaces and units are home made veneered MDF):





As I say it's absolutely critical it doesn't warp. I already scrapped the first attempt at this model after moths of work becasue of wrinkling of decks, and I couldn't live with the imperfection:



I really don't know; if this version got scrapped I would probably give up modelling altogether becasue the sheer effort needed to try and get something like this right and then have to throw it away and repeat months of work was mentally very difficult. I've salvaged models from the brink before, and as I'm sure you all know, it's not a nice feeling to see your work ruined becasue of some daft error.

How about solid wood, with a series of longitudinal slots milled in it, and metal or carbon fible strips bonded into the slots? The strips would be orientated vertically to resist bending? Whatever it is, it needs to be 100% guaranteed stable.

Cheers

05/02/2022 23:22:39
Posted by Michael Gilligan on 05/02/2022 23:18:44:

I know you ‘need’ wood, but : Slate might be a more stable alternative.

MichaelG.

Thanks Michael. I think slate or granite would be a bit heavy. Also plastic could be used, but I really want a wood finish to go with my other ship builds of the same type.

05/02/2022 23:05:46

All, I need to make a wooden base for a model ship, approx. 1000mm long x 200mm wide x 30mm deep.

The ship is a waterline model, and will be glued directly to it. The ship is made of paper and has no resistance to warping of the base.

I’d like a 5mm chamfer around the top edge.

Some people I know are suggesting plywood, veneered with the same type of upper surface wood around the sides (5mm thick to accommodate the chamfer of course).

I wonder if milling the centre of the wood out from underneath, and filling the pocket with laminating resin and fibreglass would guarantee stability? I suppose varnish may help maintain moisture content - I want a satin finish anyway.

There are other options, but I really n a guaranteed stable finish, or else hundreds of hours of work will be lost.

I notice in the instructions for the Princess Royal I’m building, the base is made up of a sheeted substructure, apparently to stop warping.

Any thoughts?

Thanks.

Thread: Hand Held Magnifiers?
05/02/2022 13:05:59

All, can anyone recommend a small magnifier for inspecting things like part centres in a lathe chuck, the accuracy of a centre punched workpiece, or the condition of a tool tip? My near point is getting ever further away.

I've got an eye loupe, but I want something that I don't need to get my head right next to the part.

I've also got a Sandvik loupe with a scale mounted under it, so you can estimate measurements, but this only really works of flat surfaces, and the scale obstructs whatever you're trying to put under it.

For scale modelling, I've got a light-weight glasses type magnifier with long eye relief, but I don't want to be putting that kind of thing on just for a quick check of something.

I've also got a larger reading type magifying lass, which it a bit bulky, and not really enough magnification. I'd think 5x-10x would be OK.

Not after anything elaborate, just a decent quality small hand-held magnifier.

Cheers.

Thread: Metal Cleaning Using Vinegar?
30/01/2022 10:15:18
Posted by Hopper on 30/01/2022 10:00:10:

The rusty old tools I have derusted with vinegar would have needed more than a little bit of wire buffing. And I never have neutralized with chemicals etc. Just washed in water then WD40, which all tools need anyways in a humid climate. Found it much quicker than using the wire wheel on my 8' grinder when doing a whole box full of tools from a garage sale etc. I did it many times when I was setting up my workshop from scratch almost exclusively from garage sales, on everything from Starrett scribing blocks to Stahlwille spanners.

For a one-off I might use the wire wheel. But I hate the way it sprays muck everywhere, including all over me. Vinegar is much more civilized for the big jobs.


If it works for you like you say, then it seems ideal. I tried the technique on the woodworking pins because I thought it would be much quicker and easier using a liquid to put them all in together, but it just didn’t work - the opposite in fact because the bright pins I’d already done went rusty. I’ve now tried several methods and they’ve all failed miserably. I guess everyone has their go-to methods and gets the hang of their foibles.

30/01/2022 09:49:50

I can’t see the disadvantage of using a brass wire wheel, brush or Dremel attachment (or a combination) to abrade the rust away. It’s much quicker, and doesn’t saturate your parts in acid. You seem to need to neutralise the acid with another chemical, abrade the remnants of the rust, buff the surface and coat with oil or WD40 to preserve the finish, so using acid just costs more and takes much longer to achieve exactly the same result.

29/01/2022 16:23:59

So I put the pickled onion theory to the test yesterday - on an old drill chuck:



Mixed 50/50 with the Sarson's white vinegar, and left in a pot overnight.

After some scrubbing with a toothbrush, rinsing in detergent, the soaking in bicarb solution to neutrlse the vinegar, drying and coating with WD 40 to get rid of the moisture remaining in all the nooks and crannies, and buffing with a cloth, this was the result:



Probably slightly worse than if I'd spent probably 2 minutes with it against a fine brass wire wheel, which would have had the added benefit of not saturating ferrous metal in acid and water.

So after the woodworking pins, and this, my conclusion about using kitchen ingredients for removing rust is that it's highly time consuming waste of vinegar - unless the only tool you have is a toothbrush. Even then, if you substituted that for a brass suede brush it would be just as good if not better.

Thread: Making a series of small aluminium cones
29/01/2022 16:11:08

So just to wrap things up - it was fairly warm today up here, so I made the cones this morning. Pretty straightforward in the end, but I still couldn't figure out a quick and easy way of parting to identical lengths. In this case it doesn't matter, but it would be good to know. I ended up parting off by feeding the GT insert into the shank, and eventually it broke free. OK there's a pip left, but again, irrelevant for this application.

They are for a 1960's vintage Airfix kit I'm building and refining - a 1:76 Bristol-Ferranti Bloodhound missile. They are shock cones for the Thor ramjets. According to a few references they are 24 degree cones, which by the look of the real things means a 48 degree apex angle (yes, my o/p drawing was wrong in this respect).

They were fitted with air pressure sensors at their tips, so I began by facing some aluminium rod, and drilling to 0.2 mm. I thought the smallest drill I had ws 0.25 mm, but not so. I used the technique mentioned on the other thread of lightly gripping the shank in the smallest chuck I had, and manually feeding it into the work:



I only broke 1 out of the three drills I had...Then machined the cone with a very sharp GT type insert:



Should really be a double cone angle, but at this size it would be invisible - the transition is pretty much in the inlet. Then machined the spigot to 1.6 mm:



The result:



After sawing off the original plastic one (actually represents a FOD cover I think), and hollowing the inlet, I Blu-Tacked one in place, with some 0.15 mm wire representing the air pressure probe:





The much smaller turbo pump intakes below the main ones will probably be replaced with brass tube for the surround, and a cut-off pin for the cone.

After congratulating myself on a job resonably well done, with the loss of only one drill, I closed the drill box lid, not realising the holder strip had come loose, and subsequently snapped my entire set of remaining PCB drills cean off.

Anyway, it was nice to get back in the garage, clean and lube the lathe, and make something from metal again. Cheers.

Edited By Dr_GMJN on 29/01/2022 16:11:49

Thread: Metal Cleaning Using Vinegar?
28/01/2022 22:10:25

OK thanks all. I've got some pickled onions, so might mix it 50/50 with the Sarson's stuff and try again on an old drill chuck I found.

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