I rebuilt the burner yesterday added more air holes in selected areas and tried to stop up the misc air leaks to see if that
would add more power. I’ll let the graph speak for itself. Note the issue at 45 or so minutes in where the temperature started to drop. At this point the sawdust bridged so badly it wasn’t feeding any fuel. After I poked the sawdust in the hopper, the temperature continued to rise. I had to continue to poke the pile to get the feed rate to be somewhat normal. Looks a lot like yesterday’s graph, so I am thinking about adding some additional air through a forced draft fan on the front end of the process. Once again the burner did do the job but slowly and until approx. 379 minutes or a little more than 6 hours into the test did the temperature rise past the point where the circulator turned on. I measured the chamber pressure, in this case vacuum and it measured .1″ H2O so additionally I am wondering if I need a larger exhaust fan as well.
Over the summer and fall I have written and tested a number of programs to have the building blocks of a working program. I knew the key this year would be the ability to log data. Of course to log data and have it mean something you have to have good data. So I spent several days working the bugs out of OpenLog, which works but I would not recommend. I also spent some time figuring out a combination of moving averages which resultx in stable data.
Of course the integration process was a train wreck. The arrays used for moving average data smoothing were declared wrong so that bug had to be found and fixed. The Serial LCD needed to be replaced, and my soldering iron wouldn’t work. A few of the functions are timed and there were some issues with those functions. The code for Open Log was not robust enough, once I worked out all those issues, which took most of the weekend, it is finally ready to test.
I had a plow in the shop for repair and soaked up the spilled hydraulic fluid off the floor with some sawdust, actually pellets that got wet. So the hydraulic oil soaked sawdust is in the hopper to be burned. It’s burning now, so tomorrow I should have some excel data which will help me make decisions to improve the software. At this point I am not sure it will be valid however, it is really taking a long time to come up to temperature with the sawdust. Another data point.
It took me longer than I would like, but the hopper/auger assembly is now painted and the electrical box is mounted and the wiring is functional. I have mounted the Arduino and LCD display. That box also contains the board that accommodates the thermistor electronics, which are the sensors that read various temperatures.
The main electrical box is a stainless steel box I picked up used from a scrap yard, putting the frugal in frugaltinker.com. That’s the reason that there are so many holes in the box, however it was such a good deal I thought it was worth it, despite the cosmetics. The cover was just too ugly to leave be, so I attempted to skin the cover with a plate which I plasma cut in “Frugaltinker.com”. This doesn’t show up too well, I probably should paint a background behind it to make it stand out better. Painting a background seems low on the to do list right now, so I think I will skip that task and focus on the burner.
The CNC was invaluable in the production of the electrical mounting plate, mounted inside the electrical box. It was great to not have to drill any holes to mount anything. All the holes were cut with the CNC and fit just fine.
So the final task is complete before the burner is welded up and tested.
I often have to cut multiple parts, so when I do, I take the opportunity to experiment a bit. In this series of cuts I changed the amperage of the Plasma cutter, a Hypertherm 45. Hypertherm plasma cutters are American made, designed and built, only about a 45 minute drive away from me. I still haven’t gotten my free T shirt for buying and registering the machine but I guess that’s another story… anyway, amazingly enough there really is not a lot of difference in the dross or slag between the three different amp settings I tried. I’ll keep experimenting to try to optimize the cut quality and speed of the CNC machine, plasma cutter combination.
The auger pipe connects the burn plate which attaches to the boiler and forms the interface between the auger feed and the boiler/burner units. I took a piece of 6″ pipe and welded it to the boiler plate and this attaches the plate to the auger feed via screws that tighten. With this assembly I can detach the auger and hopper and test a different burner simply by loosening 6 screws. Modular design for ease of design changes and maintenance.
I attached the hopper plate first because this determines the wheel height required. I slotted the holes in the saddle plates so that there is about 3/8″, or about a centimeter of adjustment up or down adjustment. Then after careful alignment I assembled the entire assembly with clamps and threaded rods. I did cut and weld in some cross pieces with gussets
This will make maintenance of the boiler, ash removal, scraping of the burner holes, boiler tube cleaning very easy by simply rolling the auger/hopper assembly out of the way.
In this step I mount the auger drive motor, it has a built in right angle drive and speed reducer which adds torque. The motor comes complete ready for wiring and mounting using four screws. Again I drew up the parts in SketchUp and then cut them out on the CNC plasma cutter, it was almost too easy. The further I get down this path the more I take advantage of the CNC’s capabilities. Note the rounded corners, I also added an extra hole on top of the motor mount plate to make adding a wire routing clip easier in the future. I remade the worm drive plate to improve some of the adjustment capabilities and added at the same time some decoration, rounded corners and used less material.
I used a Lovejoy type shaft connector to connect the motor to the worm shaft with a Buna-N spider in between to minimize any vibration or backlash to the motor, although with the worm and worm gear combination there should be none.
This step was made simple by the use of the CNC plasma cutter to make a part which I then bent up on both ends using my homemade brake. But first let’s revisit the old configuration for comparison.
I had to rob the motor and some parts from this transmission so it is in disarray but you get the idea of the complexity. It requires four sprockets, two chains, a motor and two chain tensioners. Here is a picture of the newly implemented and untested solution for mounting the worm and worm gear.
The CNC made it easy to slot the holes for adjustment, so the vertical adjustment comes from the plate to plate mounting screws, and the bearing mounting holes are slotted to get correct in and out adjustment to the keyed worm. After cutting the part and mounting it I decided what to change in the next iteration. I modified the part to round all the corners so that there are no sharp edges and extended the plate to pick up a second set of holes so the plates are attached with four screws instead of two. I think this part is perfectly functional so I won’t implement the changes but at least the SketchUp drawing has been updated.
It may seem like a small bite but step two actually requires some machining and tweaking to get correct. In this step I am going to add the auger to the pipe assembly I have already built. To do this I need to support the auger with bearings so the shaft will be cantilevered in the pipe. The auger should not touch the pipe and needs to be centered in the pipe, at least within a reasonable distance. To do this I cut some 1 x 2 square tubing and then drilled holes on the Bridgeport using the Digital Readout to measure the distance so that the bearings would fit perfectly. These particular bearings are an oil impregnated bronze bushing in a pillow block configuration. The pillow block configuration is aluminum which makes machining the pillow block easy. Here’s a picture of the key way which I machined into a piece of 1″ cold rolled. If you have the choice cold rolled is much easier to work with then hot rolled for shafts. Of course this is really not shaft stock it is round stock but it works just fine and is inexpensive.
After welding the auger onto the shaft I do the calculations to center the shaft in the pipe. To make the shaft centered I have to mill some of the pillow block bearing, as you can see in the picture I had to use a circular shim to get the auger centered in the pipe.
Finally after some adjustment you can see the end result of the auger centered in the feed pipe.
After last winter’s experience, I decided to start from scratch on the auger/hopper assembly. I varied the height several times through different burner designs. Now it looks like it was modified once too many times. The other main reason to rebuild the hopper assembly is the difficulty removing the burner from the boiler because it must stay balanced. I don’t remember exactly my thoughts at that point, I probably just had two wheels around the shop and was in a hurry.
So this fall I am rebuilding the hopper with a different auger drive system, and additional wheels and supports to make it much more robust and simple. The foundation of improvement in the new assembly is the ability to draw the parts in SketchUp as well as cut the parts with the CNC. Here’s a view of the cut out parts.
The parts laid out I call the saddle, angle iron, and side alignment plate.
The parts below are the angle iron plate with the side alignment plate. The angle iron plate is tabbed to fit into the slots of the side alignment plate, this way the parts are self aligning and jigging. Adding strength and ease of assembly. This makes the welding so much easier.
Finally here is the assembly on the welding table ready to weld, note the threaded rod, which also aids in the rigidity and ease of adjustment to make sure all the pieces are square and parallel prior to welding.
And finally the partially finished welded assembly, this assembly will be the foundation to cantilever the auger in the feed pipe as well as support the auger drive motor and gears.
The CAD designed parts combined with the CNC, combined with self jigging design for success make a nice finished assembly with light material for cost savings combined with good strength.
The plasma cutter is working in the CNC mode! I have successfully cut parts that meet dimensions and are usable. I made the plates that mate with the casters for the bottom of the machine this morning. I have them welded on and working. It was a treat bolting them together with no alignment issues without spending the time to make them on the Bridgeport.
The CNC is not finished, I have to mount the cable tracks, as well as extend some of the stepper motor wires to allow the full movement of the machine. Before I move on I want to put a coat of paint on the steel parts to make it look finished and professional. But an important milestone has been reached. This machine will allow me to make parts designed on the computer as well as improve the quality of the chip boiler parts significantly. This week I intend to finish the CNC and rebuild the hoppers support wheels. More pictures when I finish the CNC.
I restarted the boiler with a friend on Friday afternoon on the 13th of January. At present it is Sunday morning at 6:45. Thirty nine hours since starting, in that time the temperature has dropped to a low of -5°F which is the current temperature and the fuel usage has been a total of 5 bags. The house is still comfortable and has not shown any dip or problems in maintaining temperature. The only noticeable differences are two things. The lack of the oil fired boiler running which I can hear upstairs and always makes me a little twitchy. The second difference is the temperature of my office. My office is off the utility room which holds the furnace and so is normally quite warm after a cold night. Today it is the temperature the thermostat is set to maintain.
A few numbers, I paid $215/ton for the pellets, so the cost per 40 lb bag is $4.30. The hours per bag is approx. 7.8. This will need a longer time average to confirm but is probably a reasonably good number so in rough terms this is 3 bags per day for a cost of $12.90/day. I looked back to see if I had a furnace run time data which I did have a limited amount. On October 17, 2007 the furnace ran a total of 4.1 hours on a day that had a high of 51 and a low of 33 for a total Heating Degree Day of 22.7. (Heating Degree Days are calculated as (in °F) 65-(day’s max temp-day’s min temp)/2 or to restate 65-average temp) . Taking the furnace run time as 4.1 hours x nozzle rate of 1 gal per hour this translates to 4.1 gals usage for a total cost at $3.85 per gallon of $15.78 for one day relatively mild day. Yesterday’s HDD calculation using a high of 29 and a low of 11 yeilds and average of 20. So 65-20=41. Using a simple ratio of HDD/Furnace Run time would calculate to a furnace run time of 7.4 hours per day for a cost of $28.50 per day. Contrasting this with the pellet costs yields a savings of $15.60 for that one day.
So is that accurate? That was a lot of math using some not very exact calculations. The math was done correctly but Heating Degree Day calculations are notoriously rough. Many oil companies have moved onto more sophisticated methods and of course this is just a snap shot of one day. But as an reality check at this point I am confident 5 tons of pellets would easily get this building through the winter for a total cost of $1075. If I used 800 gals of oil throughout the heating season this would cost me $3080 at a cost of $3.85 per gallon. So yeah I think the numbers are reasonably accurate if not conservative. Wait until I try chips at a cost of $40/ton……too fun.