ESP-32 data logger (1): micro SD logger design

 I am backing away from the battery charger project because I need to complete another project to continue.  So far I've been using a pencil and paper to record battery charge and discharge curves.  I am going to automate that data acquisition process using a ESP-32 microcomputer.  The first attempt will be to store the data to a micro SD card.  The second version will be to use WIFI to store the data on thingspeak.com. 

I have an ESP-32 development board that I bought off of amazon.com. (link).  It's a pretty sophisticated MCU.  I program it using the Arduino IDE.  The development package is 38 pins.  A diagram of the different pin functions is shown below

The test circuit for the micro SD logger is shown below.  The circuit will be powered through the development board USB port.  I order the micro SD card module from amazon.com (link).

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The circuit is wired up on solderless breadboard as shown below, The ESP32 dev board is on the left and the micro SD reader is on the right.   The first experiment will be to simply write some data into the micro SD card and read it back. 

12V 7.2AH SLA battery (4): LM317 battery charger test

 When I originally tried a LM317 circuit, I used the circuit I found at this link.  The LM317 charger circuit is quite popular and can be found all over the web. The circuit I'm using differs from that at the above link in that I added a 100 ohm resistor in the base of the 2N3904 current limiting transistor. I did this to protect the transistor. The circuit is design for a charge voltage of 13.8V and a charge current limit of 0.75A. 

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The charging circuit works as follows: 

• The LM317 regulator controls the voltage drop between the power source on the left and the battery on the right to maintain 1.25V from the VO pin to its ADJ pin. 
• The regulator voltage is set by VO = (1+(RV1+R5)/(RV1+R5+R4)*1.25V)
• The battery charge voltage is set to 13.8 volt. Given the values in the schematic, this corresponds to RV1 = 2.52Kohm
• R6 and Q3 form a foldback current limiter circuit. The current limit cuts in when the voltage at R6 reaches about 0.6V.  If R6 = 0.82 ohms (four 3.3 ohm resistors in parallel), then the current limit will be 0.6V/0.82ohm = 0.73A. 
• In actual operation with a discharged SLA battery, the circuit will initially attempt to regulate the battery voltage at 13.8V but current limiting would cut in, resulting in constant charge current as the battery charged.  As the battery charge voltage approached 3.8V the current limiting would cut out and battery charge current would fall while the charge voltage remained constant. 

I built the charger circuit 

After building the circuit, the LM317 charger was tested as shown in the photo below.  In the upper left is a 23V source taken from the unregulated side of a 13.8V power supply. The charger circuit is in the lower left while a voltage and current monitor for the battery is in the lower right while the battery itself is in the center right. 

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The initial test of the LM317 charger is shown below.  A problem with is test is that the voltage was not set to 13.8V as required.  The voltage was set to 13.4 volts. The battery fails to charge fully and final battery charge voltage settles at 13.3 volts.  

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The test will be conducted after adjustment of the set voltage to 13.8V. 

Eclipse Viewer (Low Tech)

 

Craftsman 10" bandsaw 113.244513 (5): Testing new lower blade guide (updated)

 I installed the new lower guide into the Craftsman saw, as shown in the photo below.  There were minor issues and one major issue as noted in the photo and the list below the photo.

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• There is interference between the left side of the thrust bearing axle and the case. This is easily fixed by cutting the ends of the axle down.
• There is possible interference between the right blade guide and the case.  Fix by cutting the guide length down. 
• Change all the set screws to Allen style headless screws.  This will help reduce places to snag when installing the sawblade.
• The thrust bearing is not centered on the blade.  For now I will install a shim under the lower blade guide support to move the guide over about 1 mm. 

The saw runs fairly well, with some noise. Once I get the above issues on the lower guide fixed, I'll replace the wheel bushings with ball bearings, and replace the worn tires. 

UPDATE: 

I bought a bottom style 10-24 tap on Amazon.com for $3.  It cleaned out the set screw holes very well.  Now the set screws don't jam and it's easy to feel when the screw contacts the blade guide.   I also shortened  the thrust washer bearing axle and the two blade guides.  Now there is no interference of those features with the case.  

I printed a set of shims to use under the lower guide support to center the thrust bearing  on the blade. The shims were nominally 1mm, 0.5mm, and 0.25mm thick.  Upon actual 3D printing, each shim was 0.13mm or so larger than nominal.   The 1mm and 0.5mm shims together seemed to center the blade on the bearing the best. 

The photo below shows the shims after 3D printing.

The photo below shows the guide installed with notes on latest changes.

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Craftsman 10" bandsaw 113.244513 (4): Lower blade guide redesign (results)

This lower guide replaces Craftsman Part 69174  in the 113.24413 model bandsaw. 

I did the lower blade guide redesign in Fusion 360.  See the diagram below with changes noted.  I increased the material volume around the blade guide set screws and added holes normal to the layer plans to accommodate 2mm reinforcing screws. The holes for the thrust bearing axle were enlarged to get a sliding fit on the axle, and 3mm set screws were added to hold the axle fixed.

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I 3D printed the guide out, using black PLA, 100% fill.  Because of the black plastic of the guide it is hard to photograph. The photos below show the guide with hardware installed from a front and rear view.  

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Some notes: 

• I have not used the Cura slicer software to calibrate hole sizes while printing. All holes in the guide were slightly small. I spent a lot of time drilling out holes, experimenting on test pieces to check for correct size. 
• I was not able to use a tap well for the 10-24 saw guide set screw holes.  The tap bottomed out against the bottom of the blade guide holes. Because of this the set screws tend to jam as they get near the blade guide. That makes it difficult to feel when the set screws are solidly against the guides.
• The 2 mm tread inserts I used from the bottom for the reinforcement screws were a little tricky to install. I put them on the tip of a soldering iron and melted them into the guide body.  I had to use a screw from the bottom side  to clean out the melted plastic from the from the holes, then install the reinforcement screws from the top side. 
• I didn't use a tap on the thrust bearing axle set screws, but rather let the screws cut their on threads in the plastic.  I don't think this will be a problem as the screws don't have to be torqued very much to prevent lateral movement of the axle.   Next time I'll use thread inserts to get  better seating on the screws. 

I will be installing the guide in the saw today and testing how well it works. 

Craftsman 10" bandsaw 113.244513 (3): Blade guide redesign plans

 I bought this Craftsman 10" 3-wheel saw in August of 2023 for $10.  At the time, it didn't have the switch key or a blade installed, so the owners just sold the unit for salvage.

I found a switch key for  Craftsman products on Thingiverse.com (link).  I  then  3D printed the key in PLA, The key has to be positioned with the "legs" up while printing, and then the support material under the "head" has to be whittled off, but the switch key functions very well, as shown below. 

The saw needs new tires, but I haven't ordered any yet. I bought a 56-7/8 inch 1/4" 14TPI bandsaw blade (link) for the saw and spent some time trying to tune up the saw.   In the process I discovered that the lower blade guide to the saw was broken.   The guide body, Craftsman part 69174, is cast from pot metal, and broke at an obvious weak spot as shown in the photo below.  I found a Thingiverse.com replacement (link).  The printed out replacement part is shown below.  It was printed in orange PLA with 100% fill.  The hardware for the thrust bearing has been moved to the new PLA bearing  The blade guides were missing in the original part. I used 1/4" bookshelf pins for the side guides. 

The photo below shows the lower guide after installation. The thrust bearing has a groove in its surface and needs to be replaced. 

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The problem with the 3D printed part is immediately apparent as shown in the photo below. The blade guide set screws produce stress that is normal to the 3D printed layers.  The part is weak in that direction and the stress causes fractures parallel to the layers as can be seen in the photo. 

Someone must have experienced this problem and revised the part to be more robust (link).  See screen capture below. 

Another problem to consider is the replacement of the thrust bearing.  See the photo below and the issues list below that. 

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Thrust bearings issues list: 

1. There is no provision for moving the thrust bearing laterally to center it on the saw blade. The lateral position of the blade is mostly determined by thickness of the bandsaw tires.  I don't know how much of an issue this lack of lateral adjustment will be. 
2. The current bearing is worn with a groove on its surface.  I found replacement bearings on Amazon.com (link). They are 3mm ID X 10mm OD X 4 mm wide.  I've also found 3mm stainless steel rod to make the axle (link).  I haven't yet found material to make the spacers.
3. The thrust bearing is difficult to install on the guide. The axle is currently pressed through the guide plastic body.  I don't like guessing the proper diameter to get a good interference fit for the axle.  Also without some sort of installation jig, pressing the axle stresses the plastic guide body and distorts the part. 

My plan for the plastic guide redesign are shown in the sketch below, which is a side view of the guide: 

1. Extend the material adjacent to the saw guide set screws and add reinforcing screws to prevents cracking of the plastic when the set screws are tightened
2. Eliminate the interference fit of the thrust bearing axle and make the holes a free fit. Then add set screws to prevent the thrust bearing axle in place. 
3. Produce the thrust bearing axle spacers using 3D printing, making their lengths asymmetric to keep thrust bearing centered on the saw blade. 

I will import the bearing guide stl file into Fusion 360 and modify it as needed to get a revised part. 

Duracraft VS-312 Bandsaw restoration (7): operational test of new 3D printed gear

I modified the Fusion 3D model of the motor gear from 10.15mm ID to 10.12mm ID.  I used PLA material for the gear, 100% fill. It took 2 hours to fabricate.

To mount the gear onto the motor shaft, I first used the old gear to find the best position of the gear on the shaft. If the gear is too far up the motor shaft, the belt will wander off the wheel,  if the gear is too far down the motor shaft, the belt will get frayed on its outer edge by the outer lip of the gear.  When I found the optimal placement of the gear, I marked a short stick with a pencil to mark the height of the top of the gear from the saw case. 

To install the new gear, I first boiled some water in a tea kettle, poured it into a disposable cup, then dropped the new part into the hot water to let it expand.  After a few minutes I took the hot gear and tapped in down on to the motor shaft until it lined up with the mark for the proper height.  I had no trouble moving the gear down the motor shaft, it went down with just light tapping with a wooden mallet.

The saw was very finicky to get set up.  The three tension controls interact quite a bit.  After about an hour of getting familiar, I finally got the saw running.  I adjusted the blade position so that the blade saw teeth were slightly off the tires: 

The lower and upper blade guides are definitely worn out,  I'll cover rebuilding the guides later. 

Below is a video of a test cut with the saw: