Tooling up: getting a metal cutting bandsaw
I’ll be offering Mendel threaded and smooth rod, and making extruders. This all means cutting a load of metal rod, and some of my extruder gearbox designs will need cranked drive shafts, which means starting with 20mm diameter metal rod and machining it down.
I didn’t have any tool that would cut big rods of any material.
I considered getting a circular metal cutting chop saw, since they seem to work fast and simply on thin rods and all sorts of fairly thin walled profiles (Angles, pipes, etc). However, after substantial searching I couldn’t find any evidence that such a saw will cut big solid bars (eg 30mm diameter round let alone 100mm round). Also, most engineering plastics, such as Nylon, can’t be cut cleanly with a circular saw because the fast moving blade and widely spaced teeth tend to cause chipping.
I settled on getting a bandsaw instead. The bandsaw is far more versatile, has much cheaper blades, and was cheaper to buy too (I love ebay!).
Bandsaws come in two main types: Horizontal and Vertical. Vertical bandsaws are mostly used for cutting plate or sheets, and are more common in woodwork than metalwork. Horizontal bandsaws are mostly used for cutting long thin things (rod, bar, and profiles such as pipes and angles), and are mostly used in metalwork. After a bit of research and some hunting on ebay, I have a 12″x7″ Axminster horizontal bandsaw. The 12″x7″ means that it can cut (almost) anything that is no more than 12″ wide and 7″ tall. So I can use it to cut metal (even stainless steel) or plastic rods, bars, or bundles up to ~7″ (~180mm) diameter (which should be plenty!).
This is the most heavy duty tool I’ve ever owned, and it’s big too: 1.6m long. I’m excited about using it, and it’s a major step towards being able to do much bigger metal fabrication than I ever have before.
The new (to me) Axminster MB712 in all its glory
The saw was (as far as I can tell) in mostly good condition. I cleaned it, serviced it, fixed the cutting coolant pipe, and I’ve ordered a new No-Volt-release switch for the coolant pump, because the old one is broken – it doesn’t latch on. The total cost, including parts, was just GBP 165.
Bandsaw blades are available in two main materials and various tooth pitches and shapes.
Bigger stock and softer materials need more widely spaced teeth.
Carbon steel blades are heat tempered to a fairly high hardness along the edges to reduce wear, and left at a low temper in the middle. They are usually used on mild steel and softer materials, and are available in the widest range of sizes and tooth configurations. I got a pair of carbon steel 3 tpi (tooth per inch) wide set blades for cutting plastics. Wide set means that the teeth are bent out from the plane of the blade in alternate directions, so that the cut is wider than the thickness of the blade. This reduces contact between the blade and the stock, so it reduces frictional heating, which should reduce the tendency that plastic has to melt when you cut it. I may also use these blades when cutting large Aluminium bars.
Bi-metal blades have a wide strip of spring steel along the back and a narrow strip of HSS (high speed steel) along the front. At room temperature HSS and high carbon steel are similarly strong, but HSS keeps its hardness and strength much better as the temperature rises. This makes it a far superior tool material for cutting hard or tough stock such as stainless steel. It will also last much longer and may cut faster in softer stock (eg: mild steel or Al). I got two each of 4-6 tpi and 10-16 tpi M42 bi-metal blades.
The 4-6 tpi means that the tooth pitch varies continuously between 4 tpi and 6 tpi. This variation reduces the tendency of the blade to chatter or squeal because chatter and squeal are both resonant phenomena, and the wide variation in tooth pitch means that not all the teeth will excite all the resonances, whatever their frequencies. I think it also makes the blade able to cut a wider range of stock materials and thicknesses adequately, but I’m not sure about that.
The 4-6 tpi blade is for small stock, especially aluminium and plastic stock, and the 10-16 tpi is for 8mm steel and stainless steel rod.
I bought new blades from Just Bandsaw Blades. They were able to offer expert advice, and custom weld my Bi-metal blades in time for next day despatch. All six blades cost little more than a single aluminum cutting blade for a circular cut off saw (such as the Evolution Raptor) – Just under GBP 100 all in.
Changing the NVR switch looks like it will be pretty easy. After a bit of googling found a likely candidate on ebay, and it should arrive later today.
The broken NVR switch for my bandsaw
The cleaning and service only took a few hours, too.
Truing the vice to the blade with an engineers square
Making sure that the blade is perpendicular to the table
When I tested the coolant pump the coolant splashed onto the floor.
Coolant splashed widely when I tested the pump
I’m not sure how to stop this happening, or even if I can. I’ll try reducing the coolant flow and lengthening the delivery hose so that the coolant doesn’t have so far to fall.
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