Summer’s almost over, time to start thinking about heat

2013 Boiler design flow chart

I know it’s early on the calendar but my focus is starting to shift back to my heating hobby.  After two years of experimenting I have a proven performer with both the mechanical unit and the software I used last winter.  I could change nothing and go through the winter fairly smoothly but there is  always room for more improvement.   So this is my plan:  1) Build a new unit very similar to the proven unit I have been using but with greater feed range capability to allow the unit to feed wood chips as well as pellets.  By building a complete new unit I can always roll up the proven unit after the experiment is over and the data collected and resume heating without a hiccup.   2) Make slight modifications to the boiler to allow a larger interface plate between the feed unit and the boiler.  This will allow a greater range of experimentation with burner designs.  3) Continue making small experimental changes to the working pellet unit such as a vibrator for ash removal, different burner designs, different draft designs.  4)  Continue to make changes and improvements to the software.  To start I would like three modes of operation.  Continuous, run for some amount of time, and run until a set time.  I changed the software to run to a set time by calendar date last spring but it was built into the software by date not menu or button choice.  I would like to have the option of running for a few hours for both experimentation and also to occasionally heat hot water and be able to choose these options by menu.  This fall I am sure I would like the unit to be able to take the chill off and then shut down.    5) Build a chip dryer.  This is going to get to be a priority , I know the days are getting a little shorter and it is amazing how much less solar there is in the fall.  Time to giddy up on that one.

I know I have to prioritize the work, and work as time and cash flow allows.  But I think the first step will be to make a new interface plate and boiler opening.  This will allow standardization for the next design and this work can be done while there is no particular need for heat.  I went dumpster diving the other day and got a great new electrical box, so I guess I can get going on the that part of the new burner feed.  I like free stuff.  I may hit that dumpster again soon.

In the mean time it is still summer and there is still sailing weather.

Electrical box and paint, Step 7 of a DIY record

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  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 “”.  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.

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Adding the hopper, Step 6 of a DIY record

I built a homemade brake to bend sheet metal and it works OK, not great.  The corners are really radius’s and fairly large ones at that.  The second and main issue I have with it, is the inconsistency that comes from the bends.  I find that even though I try to align things perfectly it does not work that way.  Some of the parts I have made lately I have cut some slits with the CNC to weaken the folded edge making it more consistent and I wish I had done this for this part of the project….Anyway, a quick reminder of last years effort.

Last years hopper, auger and burner combination



As you can see the hopper is quite small and I ended up adding an extension later.  The burner is integral to the hopper and auger, making it very difficult to make any changes to the burner. Lastly the legs are welded on and have no adjustment and seriously two wheels what was I thinking?  So while the principal is the same there are some major differences.


New hopper with tabbed gussets


It’s pretty challenging to align four pieces of steel of such odd shapes and weights, so in this iteration I cut some gussets with tabs to fit into a slot in the end pieces of the hopper. This keeps the end pieces fixed from side to side because of the slot and plumb as it is butted up to the square the gusset forms.  All from welding a gusset plumb. So that was an aid to success, of course as soon as I finished I tossed some ideas around with a friend and we thought up a perhaps better way by making two peices instead of four and doing a different bending technique. Next time. In the meantime this is straight, level and functional. Almost done with the hopper/auger assembly, The last task is to mount the electrical box and paint the entire assembly while it is still apart and then assemble it into a working machine and test the auger drive.

Adding wheels, Step five of a DIY Record.

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.

Burn plate attached to auger via screws tightened 120° apart

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

Cross bars with CNC cut gussets and CNC cut caster plates

Close up of carriage assembly welded to auger tube

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.

Mounting the auger drive motor. Step four of a DIY record.

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.

Adding the worm gear and worm. Step three of a DIY record.

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.

Chain drive transmission of the auger drive, used on the last configuration

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.

Worm gear keyed to shaft, worm gear mounted on cross shaft.

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.

Adding the Auger. Step two of a DIY record.

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.

Shaft with key way machined and auger ready to weld onto shaft

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.

End view showing the machine pillow block bearings mounted onto 1 x 2 square tubing

Finally after some adjustment you can see the end result of the auger centered in the feed pipe.

Auger centered in pipe, cantilevered with two pillow block bearings