AES
Established Member
Following my piece "Hacksaws, how to choose 'em & how to use 'em + other stuff" posted here in late 2017, esteemed member "custard" raised an interesting question. In brief, he needs to cut pieces of quite hard saw steel stock (ca. Rockwell 50 hardness) into 2 inch x 1 inch (50 mm x 25 mm) rectangles. His material is approx 0.030 ins thick ("thirty thou" or 0.008 mm) and he does NOT allow any distortions in the finished piece.
In reply both I and CHJ briefly suggested a method which would meet his criteria. Since then I've tried myself and here are the results:
All custard's conditions were reproduced with the exception of material - I didn't have any thin sheet steel of Ro. 50 to hand, but my stock did reveal some 0.031 inch ("thirty one thou") steel sheet recovered from a busted ink jet printer. I GUESS this material is mild steel (it's hard to be sure, the spark test was inconclusive) but it has been very well plated (cadmium?) and from the single centre punch indent I used to test it (an automatic spring punch set to max pressure - I have no proper hardness testing gear), I believe that while it's certainly not as hard as Ro. 50, it's certainly "a bit harder" than "normal" MS sheet.
Custard did explain that his job involves filing "teeth" into the sheet after cutting to size, so even though the test piece I've used for this test is a bit softer than custard's material, I'm quite sure that all three methods I used will happily cut his material. The only problem then becomes "no dents and buckles allowed"!
The method involves making a simple wooden holding jig, then anchoring the sheet firmly top and bottom very close to the cut while actually cutting.
Rather than my usual "lots and lots of words" I've decided to try a mainly WIP photos style this time.
First the jig, as shown. It's designed to allow the job to be held above bench top level in a woodworking vice just in case custard hasn't got a mechanics vice available. It's very simply made from some scraps of ply and softwood, the dimensions being based on custard's required 50 mm x 25 mm, though of course these can be adjusted to suit whatever a job needs:
CTSM - Sketch 1 - Jig
Important is to choose one of the dimensions of the jig "table" to be SLIGHTLY LESS than one of the required finished dimensions. I chose a whisker under custard's required 25 mm as dimension "X". The second dimension ("Y") of the jig "table" is RATHER MORE than the other required dimension. For this I chose roughly 75 mm. This extra allows sufficient space for clamping.
The only other important dimension concerns the height of the "fence". This should be whatever the thickness chosen for the jig "table" PLUS about 1/8th inch (3 mm). In this case the overall height chosen was 18 mm ("table" material thickness is 15 mm).
The 5 mm thick ply "fence" does need to be square to the side of the "table" side AND at exactly 90 degrees in both aspects. Here's the finished jig, also showing the roughly 30 mm x 20 mm softwood holder which clamps the jig into the vice:
CTSM - Photo 2 - Jig
Before "parcelling" (see below), one edge of the material to be cut needs to be straight and true. In the case of my scrap piece from the printer it already had one square straight edge. If it hadn't it would be a simple matter to file one side straight and flat, if necessary, "parcelling" beforehand, as described below.
The "parcelling" simply wraps the job securely into a sandwich made up of a stiff but softish lower sacrificial piece, followed by the material itself, and finished with a sacrificial upper piece, also stiff but softish. The material could be scrap ply, thickish cardboard, or even aluminium sheet. I guess that provided they're both stiff, two different material scraps could be used for the upper and lower layers. In my case I chose some stiff cardboard approx 2 mm thick for both layers, but whatever is chosen, the important point is that it should be VERY stiff while not being too thick.
The required finished dimensions were then accurately marked on what will become the upper sandwich layer.
Good thick transparent adhesive parcel tape was used to TIGHTLY wrap the three layers of the sandwich together, making sure that all three prepared straight edges are accurately lined up. Here's the three parts of the sandwich:
CTSM - Photo 3 - Sandwich Parts
And the complete sandwich ready for the first cut:
CTSM - Photo 4 - Sandwich
As shown below, I made the first cut with a hacksaw fitted with a 32 TPI bi-metal blade and used a small triangular file to make a vee cut in the right place to start the cut:
CTSM - Photo 5 - 1st Cut Setup
CTSM - Photo 6 - Cutting 1st Cut
The results shown below look OK to me - NO dents or buckles anyway.
CTSM - Photo 7 -1st Cut Complete
VERY important is to re-tape that cut edge and then file a starting vee BEFORE relocating the job in the jig ready for the 2nd cut:
This time I made the cut with a Dremel "Speed-Clic" abrasive cut off disc in a Dremel drill running at about 15,000 rpm. I found it a little difficult to get a comfortable grip on the drill which also allowed me an accurate cut and I guess a little practice before attacking the real job would have been sensible - REMEMBER the disc's direction of rotation when working out the best grip for making accurate, straight cuts! And again do remember the filed vee cut for accurate starting:
CTSM - Photo 8 - Making The 2nd Cut
And here's the result:
CTSM - Photo 9 - 2nd Cut Complete
As before, replace the parcel tape after completing the 2nd cut and BEFORE starting the 3rd cut. This helps prevent distortions as I believe that it's the stiffness of the sandwich that prevents distortion during cutting. You'll notice in the picture that part of the lower tape/cardboard did actually break away a little towards the end of the second cut but fortunately that didn't cause any problems.
CTSM - Photo 10 - 3rd cut
As stressed above, re-taping the newly cut edge to maintain the stiffness of the whole sandwich is important. I then made the 3rd and last cut with my Excalibur 21 scroll saw using a LUX brand "Fine" grade metal cutting blade. I had a bit of a problem with getting enough blade tension to keep a dead straight line (I hadn't used this particular blade before and had temporarily run out of my usual Pegas metal cutting blades). But the result (above) wasn't too bad:
Of course, as I deliberately chose a piece of material with one existing straight line no 4th cut was necessary in this case.
The finished result is shown below (cont. on 2nd, related post).
Ah ha! Forgot, sorry folks. The limit on pix is 10, so this continues on the next post.
AES
In reply both I and CHJ briefly suggested a method which would meet his criteria. Since then I've tried myself and here are the results:
All custard's conditions were reproduced with the exception of material - I didn't have any thin sheet steel of Ro. 50 to hand, but my stock did reveal some 0.031 inch ("thirty one thou") steel sheet recovered from a busted ink jet printer. I GUESS this material is mild steel (it's hard to be sure, the spark test was inconclusive) but it has been very well plated (cadmium?) and from the single centre punch indent I used to test it (an automatic spring punch set to max pressure - I have no proper hardness testing gear), I believe that while it's certainly not as hard as Ro. 50, it's certainly "a bit harder" than "normal" MS sheet.
Custard did explain that his job involves filing "teeth" into the sheet after cutting to size, so even though the test piece I've used for this test is a bit softer than custard's material, I'm quite sure that all three methods I used will happily cut his material. The only problem then becomes "no dents and buckles allowed"!
The method involves making a simple wooden holding jig, then anchoring the sheet firmly top and bottom very close to the cut while actually cutting.
Rather than my usual "lots and lots of words" I've decided to try a mainly WIP photos style this time.
First the jig, as shown. It's designed to allow the job to be held above bench top level in a woodworking vice just in case custard hasn't got a mechanics vice available. It's very simply made from some scraps of ply and softwood, the dimensions being based on custard's required 50 mm x 25 mm, though of course these can be adjusted to suit whatever a job needs:
CTSM - Sketch 1 - Jig
Important is to choose one of the dimensions of the jig "table" to be SLIGHTLY LESS than one of the required finished dimensions. I chose a whisker under custard's required 25 mm as dimension "X". The second dimension ("Y") of the jig "table" is RATHER MORE than the other required dimension. For this I chose roughly 75 mm. This extra allows sufficient space for clamping.
The only other important dimension concerns the height of the "fence". This should be whatever the thickness chosen for the jig "table" PLUS about 1/8th inch (3 mm). In this case the overall height chosen was 18 mm ("table" material thickness is 15 mm).
The 5 mm thick ply "fence" does need to be square to the side of the "table" side AND at exactly 90 degrees in both aspects. Here's the finished jig, also showing the roughly 30 mm x 20 mm softwood holder which clamps the jig into the vice:
CTSM - Photo 2 - Jig
Before "parcelling" (see below), one edge of the material to be cut needs to be straight and true. In the case of my scrap piece from the printer it already had one square straight edge. If it hadn't it would be a simple matter to file one side straight and flat, if necessary, "parcelling" beforehand, as described below.
The "parcelling" simply wraps the job securely into a sandwich made up of a stiff but softish lower sacrificial piece, followed by the material itself, and finished with a sacrificial upper piece, also stiff but softish. The material could be scrap ply, thickish cardboard, or even aluminium sheet. I guess that provided they're both stiff, two different material scraps could be used for the upper and lower layers. In my case I chose some stiff cardboard approx 2 mm thick for both layers, but whatever is chosen, the important point is that it should be VERY stiff while not being too thick.
The required finished dimensions were then accurately marked on what will become the upper sandwich layer.
Good thick transparent adhesive parcel tape was used to TIGHTLY wrap the three layers of the sandwich together, making sure that all three prepared straight edges are accurately lined up. Here's the three parts of the sandwich:
CTSM - Photo 3 - Sandwich Parts
And the complete sandwich ready for the first cut:
CTSM - Photo 4 - Sandwich
As shown below, I made the first cut with a hacksaw fitted with a 32 TPI bi-metal blade and used a small triangular file to make a vee cut in the right place to start the cut:
CTSM - Photo 5 - 1st Cut Setup
CTSM - Photo 6 - Cutting 1st Cut
The results shown below look OK to me - NO dents or buckles anyway.
CTSM - Photo 7 -1st Cut Complete
VERY important is to re-tape that cut edge and then file a starting vee BEFORE relocating the job in the jig ready for the 2nd cut:
This time I made the cut with a Dremel "Speed-Clic" abrasive cut off disc in a Dremel drill running at about 15,000 rpm. I found it a little difficult to get a comfortable grip on the drill which also allowed me an accurate cut and I guess a little practice before attacking the real job would have been sensible - REMEMBER the disc's direction of rotation when working out the best grip for making accurate, straight cuts! And again do remember the filed vee cut for accurate starting:
CTSM - Photo 8 - Making The 2nd Cut
And here's the result:
CTSM - Photo 9 - 2nd Cut Complete
As before, replace the parcel tape after completing the 2nd cut and BEFORE starting the 3rd cut. This helps prevent distortions as I believe that it's the stiffness of the sandwich that prevents distortion during cutting. You'll notice in the picture that part of the lower tape/cardboard did actually break away a little towards the end of the second cut but fortunately that didn't cause any problems.
CTSM - Photo 10 - 3rd cut
As stressed above, re-taping the newly cut edge to maintain the stiffness of the whole sandwich is important. I then made the 3rd and last cut with my Excalibur 21 scroll saw using a LUX brand "Fine" grade metal cutting blade. I had a bit of a problem with getting enough blade tension to keep a dead straight line (I hadn't used this particular blade before and had temporarily run out of my usual Pegas metal cutting blades). But the result (above) wasn't too bad:
Of course, as I deliberately chose a piece of material with one existing straight line no 4th cut was necessary in this case.
The finished result is shown below (cont. on 2nd, related post).
Ah ha! Forgot, sorry folks. The limit on pix is 10, so this continues on the next post.
AES
