Thread: A couple of Disston #4 type tennon saws nearing completion.

Love the nice crisp lines, good job!

Originally Posted by fields

Love the nice crisp lines, good job!

Thanks. There is still some clean up to do and as these have minor cosmetic defects I will keep them for shop use.

Very nice work Rob. You have developed your own unique style of handle shape. Kudos for that.

Stewie;

Originally Posted by planemaker

You have developed your own unique style of handle shape. .

Stewie;

Thanks Stewie, The lambs tongue is still a bit of a struggle. I was thinking of the movie A Christmas Story where the little kid get's his tongue frozen to the metal pole while I was working on them. http://www.youtube.com/watch?v=_RgCbcT8eEU

Cheers,
Rob

Just doesn't seem right that one person is blessed with such skills and artistry!

Beautifully done!!

Originally Posted by artme

Just doesn't seem right that one person is blessed with such skills and artistry!

Beautifully done!!

Thanks but they're not that nice. There are a lot of little things that I want to do better. They do work well though.

A couple shots of the finished stainless backed saw.

Walnut handled 13 tpi tennon saw #2 RHS #2.jpgWalnut handled 13 tpi tennon saw #2 LHS #6.jpg

Nice saws. I'm jealous you have access to the parts to make your own saws. At this point in time I am searching all over for the spring steel for saw blanks and brass backs. For what used to be a big steel nation, it's embarrassingly difficult to find the right spring steel.

I've made one handle, I didn't attempt the lambs tongue because my tools are very limited. Good work.

Originally Posted by McDrew

Nice saws. I'm jealous you have access to the parts to make your own saws. At this point in time I am searching all over for the spring steel for saw blanks and brass backs. For what used to be a big steel nation, it's embarrassingly difficult to find the right spring steel.

I've made one handle, I didn't attempt the lambs tongue because my tools are very limited. Good work.

Thanks McDrew,

It was a bit of a struggle to put together all of the pieces. I sourced spring steel on Ebay, search for 'blued spring steel', '1095 steel', 'blued and tempered' and so on. If you can wait a while some will turn up. I am looking into other 10XX steels including 1074 and 1080/84. Both can be hardened to Rc 60+ and are apparently easier to heat treat than is 1095. I am working on the heat treating angle because I recently came into an oven and a hardness tester. I surveyed the saws I have and the hardest came out with Rc of about 43, one came out with Rc of 11! The reading is surely anomalous because the Rc tester becomes inaccurate below Rc 20 but it definitely means the saw plate is soft and it explains why this new saw from one of the custom makers is a bit of a dog. I tested an old Disston D-8 (~1920's) and it was Rc 52. I have read elsewhere that Disston saws were hardened to Rc 52. I have a couple others that I will test later in the week.
I make my backs and I have a local source for the screws that is reasonable. Look up somebody who has an automatic screw machine and is willing to do small lots.

Cheers,
Rob

Originally Posted by rob streeper

I surveyed the saws I have and the hardest came out with Rc of about 43, one came out with Rc of 11! The reading is surely anomalous because the Rc tester becomes inaccurate below Rc 20 but it definitely means the saw plate is soft and it explains why this new saw from one of the custom makers is a bit of a dog. I tested an old Disston D-8 (~1920's) and it was Rc 52. I have read elsewhere that Disston saws were hardened to Rc 52. I have a couple others that I will test later in the week.

It's been a while since I slept through my materials class, and this is outside of my field, but Rockwell hardness testing does not always work well on thin materials. I suspect that in the thicknesses and hardnesses that most of our backsaw blades are made in, a typical Rockwell hardness tester is not a reliable instrument.

This document from Instron has some guidelines for testing materials, and goes into pretty good detail. Of particular interest is the table below (Table 5 on page 13), which gives the minimum hardnesses far a given thickness that can be reliably measured with a Rockwell test.

rockwell-thickness-limits.jpg

For steel that is 0.040 inches thick, hardnesses of RC20 and greater can be safely/reliably measured. Most of the D-8's are around this thickness, if I am not mistaken, so your test on that saw may be accurate (assuming the tester is calibrated correctly).

If you want to measure the hardness of 0.025 inch thick steel, the minimum recommended hardness is around RC66, much harder than any saw plate would be. If you want to measure plate that is 0.020" or less, then you are basically looking out of luck with a standard Rockwell test in the hardness range you are looking at. I'm not sure of the thickness of the plate you tested at RC11, but this could be an explanation for the low readings.

This all assumes you are using a Rockwell tester with a Brale indenter; if you are using some other tester, then the above doesn't apply.

And, of course, these are only guidelines, so make of it what you will.

You have some interesting projects going on. I am interested in how you achieve your vacuum infusion.

The one UK supplier that says they ship "worldwide", finally got back to me and said their courier no longer delivers to south East Asia or Australia. I'll keep an eye out on eBay, thanks for the heads up.

Originally Posted by Isaac S

I suspect that in the thicknesses and hardnesses that most of our backsaw blades are made in, a typical Rockwell hardness tester is not a reliable instrument.




For steel that is 0.040 inches thick, hardnesses of RC20 and greater can be safely/reliably measured. Most of the D-8's are around this thickness, if I am not mistaken, so your test on that saw may be accurate (assuming the tester is calibrated correctly).

Hi Isaac,

My earlier post was brief and incomplete because of time considerations. Here are some more details.

Yes, I am using Rockwell C with the 120 degree diamond. Authorities differ on minimum thicknesses, some say the material must be at least three times thicker than the indentation diameter and some say ten times thicker. I know the chart you posted and use it as a guide.
I calibrated my instrument using three hardness blocks ranging from Rc 27.2 to Rc 62.2. I have a slight deviation of 0.5 Rc units over that range with the low end reading slightly high and the high end slightly low. My midpoint block is Rc 46.1 and the tester gives back that value to the limit of my ability to read the scale. The tester is Chinese and like many of their industrial products it is rough cosmetically but functionally excellent. I spent two full days disassembling, cleaning, reassembling and calibrating it.

I don't yet have a superficial hardness tester but I have my eye out for a deal.

In the following discussions I will use an asterisk next to those Rc values that are outside of the acceptable parameters for such testing by Rc*.

The Disston D-8 I measured was 0.032" thick which for Rc 52 is reported to give a valid reading, any thinner or softer and it does not.

The saw that came up with an anomalous low reading of Rc* 11 (Rc loses validity below about 20 as well) was a 0.030" thickness saw. Outside of the acceptable thickness range for Rc but not by much and given the huge Rc* difference I am pretty confident it is soft. I couldn't believe it at first either so I repeated the test, five times in the area under the handle (Perhaps the maker annealed this area, I don't know) and twice on two points at the tooth line. All readings were consistent and low.

The values measured for thinner materials will be lower, and in a non-linear fashion, due to sideways flow of the thin material when using the Rc scale. However, for materials of the same thickness it is possible to tell harder from softer plates. For the thinner plate saws I compared to 0.015" 1095 that I have which is reported by the manufacturer to be Rc ~ 48-52 and on my tester it gives an indicated Rc* of 42. I have a total of five 0.015" plate saws from two different manufacturers. I have one saw from manufacturer #1 and four saws from manufacturer #2. The plate from manufacturer #1 gives me the same reading as I observed for my 1095 reference standard, Rc* 42. Those from manufacturer #2 all gave readings of Rc* 35. Thus I conclude that the saws from manufacturer # 2 are softer than that from manufacturer #1. Not by 7 Rc units of course because I know that the scale in this region is non linear.

Since there are no systematic studies of this issue presented on this site I will post my results. I will not of course identify any manufacturers.

Cheers,
Rob

Nice saws

what are the tote's made from?

Thanks for the compliment.
These were made from a piece of walnut I had laying around. Not the best quality wood - it had a long hidden fracture. That is why the stainless backed saw lacks one of the horns on the top.

I started the handles to investigate two different techniques. First was vacuum infusion of resin to strengthen wood. In summary, it made the wood harder, tougher and somewhat more difficult to sand. No problems with rasping/filing or with finishing. Inexpensive and simple to do too.

The second effort was to investigate the use of bushings in the handle to support the saw screws, minimize play between the saw plate and the handle and diminish or eliminate the need to periodically tighten the screws. The technique works on all three counts. I originally intended to test these handles to destruction but as I progressed I decided that I liked them so no smashing.

I have yet to organize my pictures and text concluding the two threads on these handles because I am now working on heat treating and hardness testing.

Cheers,
Rob