DoAll DBW-1 Bandsaw-Blade Welder
Revision as of 22:04, 3 September 2012 by Djscholl (Updates for work progress)
This highly specialized welder is really only useful for one thing: repairing broken bandsaw blades. It is also called a buttwelder, because the technical name for the type of weld it makes in the blade is a butt weld.
- Don't try to repair bandsaw blades yet, and please don't plug in the power cord.
- Only one user adjustment (force) is required to accomodate different blade widths.
- 3/8 in. blade: "NARROW"
- 1/2 in. blade: second "M" in "MEDIUM"
- Other widths are TBD
- Vise-grip pliers are recommended for holding blades during pre-weld grinding.
- The back corners of the jaws are worn, so simply pushing the blade back into those corners is not enough to guarantee that the blade ends are parallel. It is necessary to examine the blade ends from above to manually align the back edge of the blade before tightening the knurled screws.
- The welder only has one blade thickness gauge: for 0.025 in. thick blades.
- Be gentle when checking the thickness of an unannealed weld; it is surprisingly easy to break the weld.
- Has anyone else ever repaired one of these old welders? Yes, someone rebuilt an entire 63-year-old DoAll Bandsaw, and rebuilt the welder as part of the project. Photos and written discussion are available on this thread in The Garage Journal. The URL is to page 5 of 26 pages, which is in the middle of the section that discusses the welder. The same author has made over a dozen videos of this project. They are available in the YouTube channel for APmachinist. Blade Welder Parts Repair is #14 in the Bandsaw Rebuild video series, and is one of several videos that discuss the welder. Note that the author's welder is model 1A, which is more recent than our model 1, and features different electrical adjustments, among other differences.
- Can bandsaw blades made with newer technologies (1950 or later) be repaired with this welder? Yes, if the annealing instructions from the manual for a newer model, e.g., the DBW-15, are followed.
- Continue evaluation and repairs
- Disassembly and cleaning is finished.
- Status of electrical testing/repairs
- New light socket (local lamp store) and bulb (Mouser) are installed and work at 220V.
- An electrical schematic diagram has been drawn and most of the wiring has been replaced.
- New insulators have been cut from 0.016 DMD sheet (Dacron-Mylar-Dacron from a motor shop, to replace the original waxed cardboard)
- Transformer wiring completed. Weld switch, heat switch, anneal switch, all transformer taps, appear to function OK. With 243VAC on the primary, the open secondary voltages are as follows:
- Anneal: 0.93 VAC
- Etching: 1.65 VAC
- Less: 3.00 VAC
- LessLess: 3.27 VAC
- More: 3.52 VAC
- MoreMore: 3.80 VAC
- These open-secondary voltages are higher than the nominal values listed in the manual, apparently because the nominal primary is 220VAC and our primary is 243VAC. For this reason, it is likely that the Less and LessLess heat switch settings will make the best welds in our shop.
- Replacement grinding wheel (Production Tool) is installed. It needed more clearance inside the housing, and we were able to use the wheel to grind its own clearance.
- Steve H. has made new Delrin tips for two of the adjustment screws, and both have been installed.
- Reassembly and rewiring have been completed.
- The movable jaw travel limits have been set.
- First day of welding trials
- Optimized weld stop switch adjustment based on releasing the movable jaw clamp while holding the weld lever down after welding a 1/2 in. blade. The jaw does not move, which is correct.
- Heat switch setting used for all trials was the Less setting (lowest for welding)
- Narrow force settings appeared to work well for a 3/8 in. blade width
- Intial welds on 3/8 in. blade showed an oval gap in weld. Delaying the weld stop switch by 1/8 turn closed this gap.
- An worn-out 3/8 in. blade was broken, welded, and run for about 30 min. on the bandsaw. It proved capable of cutting 1/8 in. luan plywood.
- Welds of 1/2 in. blade showed tendency of moving blade to ride over fixed blade. This is consistent with visible vertical misalignment of the moving jaw. The welder has been removed to the woodshop workbench to correct this alignment. The transformer will need to be removed to gain access to the alignment bolts.
- Second day of welding trials
- Vertical alignment of the moving jaw was completed (access required removal of motor, transformer, and transformer mounting frame). Welder returned to red shelves.
- Weld of 1/2 in. blade with force set on "SAW" showed oval gap extending to teeth.
- Weld of 1/2 in. blade with force set on first "M" in MEDIUM showed smaller oval gap.
- Weld of 1/2 in. blade with force set on second "M" in MEDIUM showed complete weld.
- A higher force step should tested with 1/2 in. blade width in the next trials.
- None of the 1/2 in. blade welds showed a tendency to make lap welds instead of butt welds, nor any other evidence of vertical misalignment.
- Third day of welding trials
- Trials with 1/2 in. blade showed tendency of moving blade to ride under fixed blade. This is consistent with vertical misalignment of the moving jaw, in the direction opposite the previous misalignment. The blade ends prior to welding are visibly misaligned. The reason why this was observed today and not in the second day of trials is not known.
- The root cause of this misalignment is not known. The next steps will be to drop the motor, remove the transformer, and study the mechanical alignment in detail. If the moving jaw alignment nuts are still tight, then there may some other part that is worn, bent, loose, etc.
- Fourth data of welding trials
- Performed careful alignment of moving jaw using both gauge blocks and a broken blade. The cause for the adjustment changing between the second and third day of trials was not found. Hoping that perhaps a welding jaw was accidently hit with a piece of lumber. Otherwise, the alignment is expected to go out again.
- Welded 1/2 in. blade with force on second "M" in MEDIUM and heat on LessLess. Weld appears to be good. Blade flexed many times by hand, no evidence of cracking.
- Box is needed to cover the parts behind the front panel
- Long-term location with 220V 1PH 30A power is needed