Power Hacksaw

Before milling or turning, stock typically needs to be cut to length. My first tool for this task was a handheld power bandsaw lashed to a plywood frame.
This worked quite well, and is still functional. The reason that I have tried other means for cutoff is that it did not do well with large (say 3 inch diameter) round stock; the blade did not travel straight in the vertical plane. Part of the reason for this is that it is still a handheld tool and it is difficult to maintain constant pressure during a lengthy cut. Also, the wood frame is too compliant.

Next I purchased a bandsaw from Little Machine Shop.
This was better because the frame was stiffer. But after a year of occasional use, the rear guide assembly failed. Again, this is still a handheld tool and I was probably forcing it too much. LMS sent me a new guide assembly and it is again working.

Large, free-standing metal bandsaws have hands-free operation and should perform better than either of these tools. They also have limit switches to shut down the blade at the end of the cut. But I do not have room in my shop for this.

If you search for “power hacksaw” on Youtube, you can find videos of many homemade saws. Invariably, they involve a crank to achieve reciprocating motion. This kind of gadget has quirky appeal; I decided to try my hand.

Here is the result.
What is different in my design is the use of a large (NEMA 34) stepper motor. This avoids the cost of a gearmotor and the complexity of two stages of belt drive.

Two more photos:


The limit switch:

The motor control: a 48 volt supply, a step motor driver, and an Arduino Nano to generate pulses at a ramping rate.

This is an auxillary fixture to hold large round stock.

Here is an extra weight for the front end, but it was too much for the 640 in-oz rated step motor.

Finally, a short video of the operation. Click on the image and you will be taken to my Flickr site, where the video can be seen.

Design and Construction Notes:
1. The frame for the saw blade is from a Stanley hand saw (STHT20138). The additional bow under blade tension is appreciable and must be considered when drilling holes in the mounting brackets, i.e., have the blade under tension when you spot the hole locations.
2. The fit of the blade end holders in the frame is loose. I was able to improve the squareness of the saw cut by inserting shim stock into the gaps.
3. The base is made from 1.5 x 1.5 inch “T-slot” material. Guide rails are 5/8 diameter steel shaft.
4. I tried Oilite for the linear bushings, but could not align well enough to prevent binding. Final bushings are teflon filled acetal.
5. The motor is rated 640 in-oz (at 5.5 amps/phase) but I think this means holding torque. The relevant rating is 475 in-oz driving at 100 rpm and 48 volts. 48 volts is much more than needed to push 5.5 amps through the 0.43 ohm winding resistance, but is needed to obtain a sufficient rate-of-change of current (4 mH/phase).
6. The motor has 200 full steps/rev but its driver is set to “microstep = 2”, so 400 pulses are needed per revolution. I run at 1.0 rev/sec, so the pulse source is a maximum of 400/sec. On acceleration, I ramp from 40 to 400 pulse/sec. I think that a 400/sec constant source would be OK (maybe a 555 timer), since there is no problem recovering from a stall when the source remains steady at 400/sec.
7. In operation, 0.7 amp is drawn from the 48 volt source, or about 34 watts. Most of this is accounted for as ohmic loss: 2 phases * 0.43 ohm/phase * (5.6 amp)^2 = 27 watts. The supply for the Arduino is just a 5:1 resistive divider from 48 volts. Wiring for the limit switch should be shielded.
8. The crank length is 2.0 inch, so the push available to the blade is 475 in-oz / (16 oz/lbf * 2 in) = 14.8 lbf. The crank grips the motor shaft with a steel shaft collar. Link pivots are shoulder screws running in bronze bushings, oil lube.
9. The two guide shafts together weigh 3.5 lbm and are nearly centered over the cutting point. Including the saw frame, the total down force at the cut is about 5 lbf. The machine runs without stall at this cut pressure. But if I add the auxillary 1.8 lbm weight at the front end (increasing the down force at the cut to about 8.5 lbf), stall is a problem. I am using a 14 tooth/inch blade, but did not see much difference with 24/inch. NEMA 34 step motors of twice this rating are available and should allow use of the extra weight. I assume that this would increase the cut rate.
10. Cutting is slow but square. I can do other tasks while the saw runs.

Here is a parts list. I have not been careful about fastener quantities, and I did not even try on small items like standard flat washers, wires, switches, etc.
Hardware list

Posted in Cutting | Leave a comment

Inefficient Use of Material

I am starting a reel with a winding plate, similar to a “Perfect”. Here are the aluminum parts.
Left: spool, 25 grams from a 233 gram blank (10.7%).
Right: frame, 42 grams from a 391 gram blank (also 10.7%).

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Faceplate for Minilathe

I was working on a new reel design, and realized that several operations would best be done with the parts clamped to a faceplate.
The problem, however, is that on my Minilathe, the carriage cannot travel far enough left to get the toolpost in position. The travel is OK for a part held in a 3 jaw chuck, but not for a part clamped to a thin faceplate. The large handwheel for carriage travel interferes with the box of variable speed drive electronics.
In this picture, you can see that I long ago added an acrylic plate as a chip shield. It also restricts carriage travel, but is no worse than the handwheel.

The first thing that occurred to me was that the electronics box needed to be relocated. It was really stupid of the designer to put it in this position.
The rack and the leadscrew are both capable of moving the carriage far enough left to allow faceplate use, it is only the electronics box restricting travel.

But then I saw that it would be much easier to just move the handwheel.

So I made this extender for the handwheel shaft.

Here the extender is installed.

I made a 4 inch diameter faceplate on my mill.

Here is the faceplate installed and finish turned.

Posted in Fixtures, Turning, Work Holding | 2 Comments

San Juan River

Was at the San Juan yesterday for the first time, did a float trip from Texas Hole to Crusher Hole. That must be the standard route, as there is even a shuttle service to spot the guides’ vehicles and trailers downstream.
It is a tailwater fishery. Water was clear; I have never seen so many trout. They get fat on the abundant midge life coming out of the bottom draw of the dam.
It is bobber fishing over tiny nymphs. I had a “San Juan Slam” of rainbow, cutbow, and brown. Many hookups, many brought in, most of nice size. Guide Scott Warren of Durango CO.

Posted in Uncategorized | 1 Comment


My family took an Inner Passage cruise. Son-in-Law and I used the Juneau day to go fishing. I did not research what to do ahead of time, we just signed up with the Cruise Line standard. Bear Creek Outfitters and guide Sam did a fine job: supplied waders and rods, and tied all knots, etc. Also carted the special items needed for Alaska fishing: satellite phone, bear spray, firearm.

We flew out on a Beaver to Slocum inlet and then slogged our way up the creek.

Sam gave us Clouser Minnows, but of colors that I never saw in Michigan. A “school” of Cutthroats and Dolly Varden readily took these streamers. A little father upstream were Pink Salmon, and they wanted the Clousers also.



Granddaughter clearly does not believe my lie about a big fish.

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Ball Turning

My “standard” bronze frame reel has two surfaces that are cut to a spherical shape, one is the spool retaining screw head (convex) and the other is the waist on the knob (concave; at least, concave motion of the cutter). When I had a Sherline mill I could use it as a lathe by turning the headstock 90 degrees and mounting the cutter to a rotary table. But now I have the more robust Mini Mill, and axis of the headstock can only be vertical. It is still possible to turn, but it seems quite awkward.

So I sought a way to do the turning on my Mini Lathe. First I bought the standard ball turning tool:
But it failed on both counts; it was not big enough to make an 0.8 inch convex radius or a 1.8 inch concave radius.

On Pinterest, I have been seeing many home made ball turning tools. So I have made my own, of a generally similar design.
The cutter is a 3/8 inch round carbide insert.

Cutting a convex surface – screw head.

Cutting a concave surface – knob.

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Tool Post Grinding

I have been selling “Ferrule Shrinking Tools” again; they are used by bamboo rod makers to reduce the diameter of a female nickel silver ferrule and improve the fit. Since I have pretty well satisfied the total rodmaker demand for this tool, it is hard to justify ordering another large batch of parts from a machine shop. So I decided to make a few myself.
The main structural parts are two aluminum disks, 2-5/8 diameter and 3/8 inch thick. The slabs are sawn from a 2-5/8 rod and have to be faced off with a lathe.

I did the facing with my Minilathe because the Sherline lathe does not have enough low speed torque, making the operation very tedious. But the faces of the disks were coming out about .004 inch out of parallel. This would be OK for the purpose, but I felt that I should be able to do better.
It is easy to see why the disks vary in thickness; the height of the three chuck jaws vary by a total of .004 inch.

So the chuck jaws need a little adjustment. But these jaws are hardened and cannot be trimmed with lathe bits that I have. This a a job that calls for a tool post grinder. Not wanting to lay out money for the real thing, I decided to try my Dremel tool.
Instruction on how to do this are on Varmit Al’s Mini Lathe Page. First step is to square up a Dremel-sized stone. I did this with a diamond point tool.

Here is the grinding setup. The chuck jaws are clamping a scrap disk so that the jaw surfaces that I want to trim are at the right radius. The Dremel tool is held in a bracket that I made a long time ago for use with a Sherline mill. All 3 jaw surfaces have been colored with a Magic Marker. I turned the chuck by hand.
Since I have removed the compound assembly in order to mount the Dremel tool, I have to advance the stone using the lathe’s rack drive. A dial indicator shows the carriage axial location. A clamp for the carriage is needed, also described by Varmit Al. I had to take very light cuts, about .0003 inch, or the Dremel tool would stall. But the final result was quite satisfactory.

Posted in Abrading | 2 Comments