Harold Hahn

[Dave Stevens (Lumberyard)]

rather than use a table saw or the blank jig HMH used i cut the blanks apart with a band saw and no concern for accuracy



The accuracy is when the angle is sanded i set the miter to the angle using the cardboard pattern and sand the angle. This does involve an extra step as opposed to cutting the angle on a saw. I never cut blanks on a table saw because i do not have a large table saw just a 4 inch Jarmac and that did not work so well. and i do not know if you can get a smooth enough cut with a saw as apposed to sanding.

 

[Dave Stevens (Lumberyard)]

The use of the jig for cutting the blank pieces is to hold the wood in place to get a straight cut every time. Cutting pieces freehand you do not have to worry about the stock being a consistent 1 inch wide.

In this photo the bottom piece was sanded freehand. By not holding the piece absolutely steady and at the same angle the piece will rock causing a rounded edge.



The black line is the angle line you want to sand to. if your piece is not exactly parallel to the sanding disk and you start sanding then shift the piece the slightest movement of your hand will cause a pivot point at the arrow. The blue line demonstrates the two different angles you end up with rather than one straight continuous edge.



Another way is to use a table saw by setting the correct angle and slicing off each piece. Small hobby size table saws have thin blades that tend to move or wobble and it takes the slightest movement of your had to mess up the cut. So by using a table saw is not a sure fire way of getting a perfect cut edge. The pieces were cut on a small table saw. If the piece is not held tight against the miter guide the blade will either gouge or cut in a step pattern. Under powered mini table saws will chew through the wood leaving an uneven cut



one reason i guess why HMH used a full size table saw is to insure clean straight cuts for a perfect joint between pieces

 

[Dave Stevens (Lumberyard)]

C clamps or spring clamps work the best for clamping the frame halves together. Putting the frame underweight does not work as well as clamping because it requires more weight than you would expect. Clamping a frame blank as shown here will result in a fit as shown in the next photo.




the outer edge is wide enough to slip a business card into the gap. When building frames with the blank the wood tends to warp side to side in a slight arc called cupping.
The next photo shows a frame blank clamped to the corner of a piece of plate glass. The number of clamps prevent the wood pieces from cupping and also by clamping the blank to the glass keeps it flat and free from any twisting.



a properly clamped frame blank the seam is barely noticeable

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[Dave Stevens (Lumberyard)]

Using rubber cement the frame pattern is glued to the wood frame blank. It may not seem so but this step is important you get the patterns glued to the blank correctly. A common error is to cut the frame pattern like this. Actually, it is the logical way to go because you can see the inside and outside edge of the blank to position the pattern.


The paper pattern is flimsy enough that if you look close in the upper right corner at the yellow arrow you can see the pattern can move as much as quarter inch unnoticed. This will throw off the shape of the hull



ideally you want to keep the inside of the drawing intact this maintains the shape with little to no distortion

 

[Roger Pellett]

Back in the 1970’s the Sears Roebuck Company sold a saw blade that they called a “Kromedge Thin Rip Veneer blade.” This was a seven inch or so, fine toothed, hollow ground blade. The teeth were not “set” like an ordinary saw blade. It would make beautifully smooth cuts in hard woods. I still have one.

Harold Hahn specifically writes about using this particular blade to build his models and one is shown in the third photo of Post #99 that Dave posted above. Unfortunately, the specific blade is no longer available although they occasionally show up on EBay. When shopping for a saw blade to build a model using the Hahn method try to buy one with the same characteristics as the Kromedge blade that I described above.

Dave does not mention it specifically but many of Hahn’s models were built before the advent of the Byrnes saw. He used an ordinary 8” saw fitted with the blade that I described.

Roger

 

[-Waldemar-]

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Back in the 1970’s the Sears Roebuck Company sold a saw blade that they called a “Kromedge Thin Rip Veneer blade.” This was a seven inch or so, fine toothed, hollow ground blade. The teeth were not “set” like an ordinary saw blade. It would make beautifully smooth cuts in hard woods. I still have one.

Harold Hahn specifically writes about using this particular blade to build his models and one is shown in the third photo of Post #99 that Dave posted above. Unfortunately, the specific blade is no longer available although they occasionally show up on EBay. When shopping for a saw blade to build a model using the Hahn method try to buy one with the same characteristics as the Kromedge blade that I described above.

Dave does not mention it specifically but many of Hahn’s models were built before the advent of the Byrnes saw. He used an ordinary 8” saw fitted with the blade that I described.

Saw blades with exactly these characteristics are called milling blades here, are widely available and are normally used in production environments for cutting and making narrow grooves in metal. They come in a wide variety of sizes (diameters), thicknesses and tooth densities. They are usually made of HSS, but there are also entirely carbide variants (bottom left in the picture).

Obviously, these saw blades are also capable of making perfectly precise and smooth cuts in wood, provided that the cut is not too heavy and the set-up is precise. Otherwise, they could easily ‘burn’ the wood.

As far as I know, Byrnes installed exactly such imported cutting discs and even from my very part of the world in his table saws as standard, which at the time caused a certain amount of outrage, or at least great surprise, among his customers .

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[rfuh47]

The Sturm CS5060MS was once popular.
You could try its discs.

 

[rfuh47]

When sawing with a jigsaw, reverse-tooth blades are very useful. They minimize chipping.

 

[Dave Stevens (Lumberyard)]

Roger i inherited a Sears Roebuck 8 inch table saw from my dad a big heavy tool and i did have one of those blades. The table saw was one of those tools that sat unused more often than used and it took up a lot of space so i got rid of it.



i did try the hobby size table saws and they were just too small and underpowered to rip 225 liners feet of hardwood framing stock. They were like using a toy compared to a full size 3/4HP Sears table saw.

For someone wanting to build a Hahn POF model what kind of advice can one give?

to cut out the frames a table saw is unless you need a scroll saw or band saw. It is too expensive to buy both. band saw blades come in a number of TPI so you can get a smooth cut on a band saw.

needing a disk sander to finish the frames depends on how you build the hull, looking at models under construction by Harold each frame was finished to perfection before they were added to the framing jig.

 

[Dave Stevens (Lumberyard)]

There are two methods for building a hull. One is to cut and finish each and every frame then install it into the hull like Harold did. The second approach is the cut the framing a little over size inside and out except for the extensions that fit into the jig and cutting the notch accurately the rest of the frame can be left unfinished. The hull is built with the oversize frames and once all the frames are in place the hull is sanded and shaped. The second method is giving some leeway in both shaping the frames as well as building the hull. In the first method everything from the first step has to be done exact or nothing will fit as the hull is built

roughly cutting out the frame if your careful you can cut the shape without needing to sand the frame



or you can rough out the frame and sand the frame shape close to the final finish just leaving enough material for the final sanding of the hull.

 

[Dave Stevens (Lumberyard)]

before moving on with the story of Harold Hahn lets drift into the pros and cons building a hull then shaping it or building a hull from refined finished frames. I think finishing the frames first is very difficult as opposed to rough shaped frames and shaping a hull. What is called "dubbing" How close from original draft to the mold loft to the patterns used and the final build in the yard how much was done to a hull while under construction?
To follow actual ship building practices in model building is not always practical. Is model building like electricity seeking the path of least resistance?

 

[-Waldemar-]

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before moving on with the story of Harold Hahn lets drift into the pros and cons building a hull then shaping it or building a hull from refined finished frames. I think finishing the frames first is very difficult as opposed to rough shaped frames and shaping a hull. What is called "dubbing" How close from original draft to the mold loft to the patterns used and the final build in the yard how much was done to a hull while under construction?
To follow actual ship building practices in model building is not always practical. Is model building like electricity seeking the path of least resistance?

Similarly, in my opinion, following real-life practices in model construction is simply pointless in normal situations, unless it is an end in itself for some specific reasons.

Nevertheless, I wanted to take this opportunity to show a fragment of a plan from the mid-18th century, which I should have shown earlier, but forgot about. It concerns the precision that was practically achievable at that time.

The designers of this ship decided to modify its shape still at the design stage. They started by raising the longitudinal design line by two inches (visible as a dashed line parallel to the continuous one on the side projection), which caused corresponding changes in the contours of the frames (visible on the body plan) and waterlines (visible on the top projection). I have taken some measurements on this plan, and it turned out that the resulting modifications to the contours of the frames are mostly within the range of only 1 to 2 inches (only in a very few places it reaches about 3 inches).

The point is that — since the designers worked with such high precision, it was not so that the loftsmen could later create their own design for this ship, by deviating from the designed lines by more than a fraction of an inch.

Admittedly, this is the reality in the English professional environment, but there is no reason to believe that professionals in other parts of the world followed any inferior standards.

The plan in question (British archives; J2656; ZAZ1341):

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[Dave Stevens (Lumberyard)]

Nevertheless, I wanted to take this opportunity to show a fragment of a plan from the mid-18th century, which I should have shown earlier, but forgot about. It concerns the precision that was practically achievable at that time.

precision in design and drafting is one thing. As an example in building the Sir Edward Hawke. On paper everything is right on the mark but in practice that is when things go off.

The point is that — since the designers worked with such high precision, it was not so that the loftsmen could later create their own design for this ship, by deviating from the designed lines by more than a fraction of an inch.

i agree the designers may of worked with such high precision but did that translate to the yard and the hands on building process? both in scale model building and real ship building. A builder such as Hahn was an engineer an artist and skills above and beyond the average model builder. He went from drawing to build within close tolerances. But is that practical for the average model builder?

I have read through archeological field reports and framing was random spacing give or take a few inches, timbering sizes had a range of up to 3 inches.

 

[-Waldemar-]

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i agree the designers may of worked with such high precision but did that translate to the yard and the hands on building process? both in scale model building and real ship building. A builder such as Hahn was an engineer an artist and skills above and beyond the average model builder. He went from drawing to build within close tolerances. But is that practical for the average model builder?

I am not sure if there is any reason for dispute in this particular matter, and in fact I am quite sure that there is not. I am absolutely aware that in reality the quality of work at all stages of a project can vary greatly, and this applies to both the distant past and the present day. I think I can say that my general intention is rather to demonstrate this diversity, as opposed to sticking to a single scenario of inevitably inaccurate work that has to be corrected at each subsequent stage.

I have read through archeological field reports and framing was random spacing give or take a few inches, timbering sizes had a range of up to 3 inches.

Here, in my opinion, the matter is more subtle. Incidentally, I even consider it a kind of trap that proponents of building ships by eye fell into, and that, in their opinion, these ships had to be characterised by sloppy lines for this very reason. Yet, after all, the two do not necessarily have to be related, since it is entirely possible to build very precise structures using elements of irregular dimensions and irregularly spaced. An iconic example of this is the Egyptian pyramids, built from stones of very different sizes, yet as a whole they have very regular shapes and are precisely aligned with the cardinal directions or celestial bodies. On the other hand, it is entirely possible to mess up the general shapes of a structure even when using perfectly regular elements in terms of their arrangement and, for example, their thickness.

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