Scratchbuilding questions

[Jack P]

Hey guys,

 

I'm trying to cut my own frames for a project and starting to run into difficulties. I certainly didn't expect everything to be smooth sailing, but my first attempt is only really fit for the bin. I have a few questions that hopefully those that know can help me with.

 

1: How do you cut a straight line? I've got a properly tensioned jewelers saw with a new blade in it but my straight cuts wander. Do I need to scribe the line deeper so that my cut has something to follow - or should I butt the work up against something and use that to guide the blade straight?

2: When you're measuring and transferring drawings, should you be measuring from the inside, or the outside of the line? Or - does this not matter, you just have to choose one and commit to that

3: In the same vein - when you cut the line, are you supposed to cut the inside or the outside of the line?

4: Cutting corners (not literally), is there any particular trick to this, or is it just a case of practice, practice, practice?

5: Tools, I've got a bench pin, vice, jewelers saw, a scribe, a few assorted rulers and an engineers square - is there anything else that might be classed as either 'Essential' or extremely helpful that I could add?

6: Tips and tricks, is there anything else worth knowing or trying, suggestions for a novice? I've read through Geoff Holt's books on scratchbuilding, and it's fantastically inspiring, but i'm having a little difficulty putting it into practice. 

 

Thanks in advance!

 

 

 

 

[Jeff Smith]

You would stand a better chance of cutting a straight line with a flat hacksaw blade, junior or regular.  I would cut on the waste side of the line as close as possible and finish off filing down to the line.I

 

Also you should cut, or at least finish filing the profile with the two frames bolted together, and drill the axle holes or hornblock cutouts through both to ensure the locations are the same.

[Jack P]

19 minutes ago, Jeff Smith said:

You would stand a better chance of cutting a straight line with a flat hacksaw blade, junior or regular.  I would cut on the waste side of the line as close as possible and finish off filing down to the line.I

 

Also you should cut, or at least finish filing the profile with the two frames bolted together, and drill the axle holes or hornblock cutouts through both to ensure the locations are the same.

 

Ok excellent, I work across the road from a hardware store so I'll nip across and grab one later today. 

 

I folded the sheet metal over at the top and then soldered it along the bottom, it definitely aided with getting everything the same on both sides. 

[Jeff Smith]

So what thickness material are you using, it sounds thin.  The normally accepted practise for sawing metal (and other materials) is to have a least two saw teeth within the thickness otherwise it will just judder.  This is why there are some very fine blades available for coping and jeweller's saws.  You can bend this rule by angling the blade......

[Jack P]

12 minutes ago, Jeff Smith said:

So what thickness material are you using, it sounds thin.  The normally accepted practise for sawing metal (and other materials) is to have a least two saw teeth within the thickness otherwise it will just judder.  This is why there are some very fine blades available for coping and jeweller's saws.  You can bend this rule by angling the blade......

 

I'm using 0.015 N/S. I put the metal in my folding bar and levered it around, using my vice to finish the fold off.  I've also got some 0.015 Brass, and 0.022 brass. I'm not having too much trouble with the cutting part, just keeping the line straight. I picked up a Stanley Hacksaw and some replacement 32T blades. I'll give this a go when i'm home

[Barclay]

Hi a well scribed line should guide a blade if it is fine enough. Can I ask what size blades you are using? I would use 5/0 for thin metal like this. You'll be lucky to get it dead straight though so allow a small extra amount for waste, so it can be draw filed until straight.

 

However for cutting out the basic frame blanks and any other fairly long straight cut I usually score with the scriber until it just shows through to the other side, then score the other side several times too. At this point you can put it in a smooth jawed vice and use a steel ruler to bend it back and forth until it breaks. 

[doilum]

Hacksaws. The name tells you what you need to know.

Try a variety of piercing saw blades cutting outside of the line. It can help to make a plywood support plate that clamps to the edge of your work table. This should have a long slot cut into it and will support the work. Small G clamps will keep the workpiece steady and you now have a chance to cut straight lines. If the work is more than 2mm thick the hacksaw might be the answer.

Confession Time. I feed thin sheet brass on a sacrificial piece of hardboard through the band saw leaving a good millimetre which can be trimmed back with a Dremel. I still have ten digits!

I tend to make frames from strip brass using the machined edge at the top. This avoids the need for very long cuts.

Edited September 22, 2020 by doilum
Additional information

[ikcdab]

Scribe a decent line with a sharp point. It helps if you colour the metal with a marker first, then the scribes line will show up better.

Always cut to the outside of the line.  In theory, the line should just be visible when you are completely finished. 

Then cut with a fine tooth saw. Don't go right up to the line,  but leave a littke margin, say a mm or so. Take slow cuts with a fine tooth saw. The deeper the blade, the better as that helps keep it straight. Go slowly and keep checking all the time that you are on target. If the saw wanders, you can carefully "steer" it back on line. It helps if your body is directly behind the saw.

Being able to hold the material very firmly in critical, a clamp of some sort is what you need.

Once sawn, mount in the vice and gently file to the line, again checking constantly that it is square and to the line.

If cutting two identical pieces, bolt or solder them together first and cut and file as one.

Hope this helps

Ian

[34theletterbetweenB&D]

13 hours ago, Jack P said:

2: When you're measuring and transferring drawings, should you be measuring from the inside, or the outside of the line? Or - does this not matter, you just have to choose one and commit to that

 

4: Cutting corners (not literally), is there any particular trick to this, or is it just a case of practice, practice, practice?

5: Tools, I've got a bench pin, vice, jewelers saw, a scribe, a few assorted rulers and an engineers square - is there anything else that might be classed as either 'Essential' or extremely helpful that I could add?

2. It is a counsel of perfection, but avoid measuring off drawings. The quoted dimensions are constant, in a way that what can happen in printing processes and to the paper over time are not.

 

Where the drawing is the major or only resource as a guide to dimensions, take the time to dimension it from any overall dimensions (even if these are estimates) that you have, checking the arithmetic as you go so that the overall dimension is consistent with those that must sum within it. Establish at this stage what you will use as the datum lines and points for measurement for each axis.

 

4. Finding the right technique, and then practice in execution. It was something of a proverb back in the day that the best scratchbuilds concealed much patient 'cut and try'.

 

5. Good lighting; and magnifying visors, close vision spectacles and the like, are useful aids as the eyes get older...

[DGO]

7 minutes ago, 34theletterbetweenB&D said:

2. It is a counsel of perfection, but avoid measuring off drawings. The quoted dimensions are constant, in a way that what can happen in printing processes and to the paper over time are not.

 

Where the drawing is the major or only resource as a guide to dimensions, take the time to dimension it from any overall dimensions (even if these are estimates) that you have, checking the arithmetic as you go so that the overall dimension is consistent with those that must sum within it. Establish at this stage what you will use as the datum lines and points for measurement for each axis.

Whenever possible do not measure from Paper Drawings 

 

Many years ago I worked on some original QE2 Drawings for her last refit, we scanned in the original shipyard drawings that had at some point got damp, when we measured off of those drawings there was a 2.5 foot difference between one side of the hull to the center line compared to the other side. Fortunately we only needed the drawings as a guide as we were involved with fitting new interiors to the cabins. But it shows what can happen when plans get damp.

[Siberian Snooper]

I was taught as an apprentice to always measure from a datum to avoid compounding errors and always cut on the waste side of the line, as you get more proficient you can get fairly close to it. For the likes of horn guides, I would drill a hole slightly undersized at the blank end, make sure that the drill line is just over half the drill diameter, so that you can finish by filling up the line. Also finish corners with a triangular file.

 

HTH.