I now regret the optimistic conclusion to my last post! – the sanding and finishing process is neither quick nor easy. Each baffle has required a good hour and a half of patient hand sanding, working down to 150G to achieve a good surface prior to oiling. The top of one of the baffles had quite a bit of shallow pitting in the grain (see close-up in previous post) which needed a lot of elbow grease with the 80G paper to rectify. Both still have some minor imperfections but these will be covered by the tweeter baffles.
The photos show the sanded baffles before and after the first coat of Osmo Polyx – I am using the 3032 satin matt I had left over from a parquet floor redo. Both baffles have some interesting U-shaped curved grain which is very pleasing – see close-up.
The only drawback with using hardwax oil is the drying time; the first application with brush takes a good 24 hrs or more to dry before the other side can be treated. More patience required… after smoothing off the first coat I am planning to apply a further two coats, although these will be rubbed in/off with some lint-free rag.
In the meantime I have sealed and sanded all the hardboard components with MDF sealer, primed these with the Bedec primer, and put a further coat of primer on the front flap of the woofer boxes – I should be able to start with the black paint soon.
I had a good couple of hours uninterrupted work on the baffles this evening (lady wife having retired to bed early) and made good progress. The second baffle is now drilled. I decided to start with the UM hole first to get it out of the way. Shallow marker cuts with the big Forstner first, then waste drilled out completely – I anticipated the Forstner would have no trouble dealing with the remaining thin ring of waste.
Wrong! Even this was too much for it – the photo shows how far it got before I abandoned it in favour of the jigsaw followed by the drum sander. End result cleaner than baffle one. The moral for any prospective builders is: if money is no object buy a high end 3 1/4″ Forstner for the UM driver hole – if you feel you’ve spent enough already on your LX521 project use a jig saw and a drum sander!
By contrast the tweeter holes were a doddle this time, and their baffles were tidy using the two stage drilling plan. I then cut the lower midrange holes using the jigsaw, carefully noting the grain direction around the marked circle first to keep all jigsaw runs with the grain – this required four separate runs in differing directions. Back to the drum sander to tidy up and bring back to the line.
With the holes completed I did a trial mount of the midrange units to mark the fixing screw positions. I’m using black No 8 self-tapping button head pozi screws for both units (Accuscrews again), but if I made another pair I would definitely use No. 6 for the UM driver; the screw holes are very close to the margins of the driver hole and one of my holes cut out ever so slightly with No 8 guage. Rock solid still, but a tad untidy; it needs a small glue repair.
With all mounting holes drilled (bar those for the M6 bolts that screw the baffles to the supports) it was time to cut out SL’s angular baffle shape. I planed the top and bottom edges first so no worries about splitting. Thankfully my jigsaw was in genial mood today, and I was able to cut the side edges to within a millimetre without incident – again ensuring all runs were avoiding cuts into end grain.
The long lower sides of the baffles can be planed, but because of the shape of the upper part of the baffles I will have to rely on hard work with the sanding block for all other edges.
Cutting the baffle outlines revealed a small dowel hole in the bottom edge of one of the baffles; I was expecting this as when experimenting with a dowel joint for the panels I miscalculated a dowel hole depth. I fashioned a small round peg from the adjacent waste and glued this into position, carefully noting the grain direction first; this should be all but invisible once planed off and sanded.
I finished the evening by sanding the edges of the first baffle, initially with the drum sander, and then moving on to 80G paper. This was hard work, but the sanding block took out the residual unevenness left by jigsaw and drum sander better than I was expecting. I’ll return to the edges with finer grades in due course.
With the waste removed my drill press could now reach the position of the mounting bolt holes, so I drilled these next, and did a trial fit to the baffle support bracket. To my relief all bolts engaged without undue difficulty in the brass inserts – one is rather stiff however and I think some grease or soap is in order. After countersinking I reassembled, and took my final photo.
I still have to drill wire runs between the two tweeter holes; other than that, all this baffle now needs is its final sanding and some Osmo Polyx wax oil, and it will be finished.
To cheer myself up after the Forstner fiasco I brought the first baffle panel indoors together with the tweeter baffles to assess the fit of the tweeters / upper midrange units.
I’m using dainty little 3/8″ No 6 black self-tapping pozi screws from Accuscrews to attach the tweeter baffles; the screws for the front and rear baffles share the same through-holes so if they are much longer they will collide.
All is well! – I was particularly pleased that my 19mm cherry ensured adequate clearance at the back of the tweeters. These are secured by black M4 8mm bolts inserted through the centre of the opposing baffle, and gratifyingly the tweeters lined up perfectly with the pre-drilled baffles. I knew from the support / build forums that tweeter clearance has been an issue for some builders using 18mm materials. I have sufficient clearance to allow the insertion of small foam grommets between tweeter and baffle to insure against any rattles at final assembly.
I still need to drill the mounting holes for the upper midrange on this baffle – but first I need to cut the lower midrange recess and set about baffle two…
Today I drilled tweeter and upper midrange mounting holes on the first baffle. A character-building experience…
To ensure the best alignment I decided to drill the tweeter holes with the appropriate tweeter baffles screwed in place; I reckoned the easily drilled hardboard would also steady the Forstner bit as it started to attack the cherry.
This ploy worked pretty well, but after the first hole I realised that once the hardboard cut was established it was better to then remove the tweeter baffles to avoid their holes from fraying. The first tweeter baffle hole was somewhat furry therefore, however this will be hidden under the tweeter flange so not a concern. Two clean hardboard tweeter holes… So far so good.
The fun started with the large 3.25″ bit I had purchased months earlier with the tweeter bit. Using my Bosch drill’s slowest speed setting (around 300rpm which for hardwood is admittedly faster than ideal) the initial circumferential cut was nice and clean. However the central cutters made virtually no impression on the wood between centre and circumference.
Increased pressure via the drill press was limited by stalling the drill, the drill lifting out of its mounting, or both, and despite regular pauses to lift and rest the bit progress was very slow. It was also accompanied by a fair amount of smoke, firstly from the wood surface, and secondly from the drill! Rethink required.
Clearly the large Forstner was not up to the task, and to be fair neither were my relatively light weight drill and press. Not being prepared to part with big money for a Colt bit I will only ever use twice, I initially honeycomb drilled the waste prior to a further assault.
These modifications produced better progress – although I chewed the hole edge in a moment’ s loss of concentration I reached a depth of around 15mm before the incendiary risk broke my nerve. I used the jigsaw to remove the remaining disc of waste befor returning to my trusty drum sander to finish off. End result… acceptable – some further loss of pride re workmanship, but in the end no-one will know – the midrange unit will conceal the tatty edge.
Thinking about this “learning experience” whilst consuming a Franco Manca sourdough pizza, I have decided on the following strategy for baffle two:-
Drill through-hole at centre
Honeycomb-drill waste to within an inch of its life
Perform initial circumferential cuts from BOTH sides with Forstner
Proceed if bit decides to cut; otherwise remove waste with jigsaw and finish with drum sander
Initially I had planned to assemble the cherry boards with dowels to add strength, but after an experimental first joint decided to ditch the dowels; despite my most careful mark out the joint was slightly out of true. I had not realised how easy my new aluminium clamps would make the procedure, as these supported the boards perfectly during glueing. I left them clamped for several hours after which joints were rock solid and well aligned, requiring minimal planing off to achieve an impalpable joint line.
One baffle panel has a minor concavity because of a slight warp on the main central board, so I planed down the side boards by about 0.5mm to reduce this. It certainly won’t be noticeable without getting a straight edge out and I don’t anticipate a problem when it comes to mounting the drive units.
Once the planing was done I was able to retire to the kitchen to finish all the marking out. I plan to have all drive unit and screw / bolt holes drilled and and prepared before cutting out the finished baffle shapes – another job I am apprehensive about!
Today I made the tweeter baffles. These are fiddly because of the lower curve that frames the upper midrange unit, and I was a little apprehensive about how to obtain a neat job.
I first cut out the baffles with a Stanley knife and a metal ruler; the 3mm hardboard needs 8 – 10 passes with increasingly firm pressure to cut very cleanly. I then clamped all four baffles together and rough cut the curves with the jigsaw. I then gently took the hardboard back to the curve line using my trusty little Screwfix drum sander mounted in the drill press. This has been an excellent buy and has rescued several awkward moments. In the end the job was far easier than expected and they all came out neatly.
All that remained was to cut the bevels at the lower edge for the front facing baffles; I adopted Bill Schneider’s idea of giving the rear baffles a different look. The final task was to lightly bevel the top and sides with the plane. Really pleased with how they came out.
I’m keen to get on to the hardwood baffles, so before finishing for the day spent some time marking out my 7.5″ cherry board (which I had bought months earlier at the same time as the drive units) for the two panels; this will involve cutting and glueing two short 3″ wide boards to either side of the lower ends.
The last couple of days has seen further work on the baffle supports – these are now all screwed and glued and (bar the Speakon brackets and the small hardboard covers) sanded and primed. They are looking good.
Glue-up had to be a staged affair (though not as laborious as the woofer boxes!), the main challenge being to ensure the sides were nicely square to the bases. The hardboard components are also shown here; the spacer is screwed onto the hinged element, and the narrower piece will go behind the front plywood components to retain the head of the bolt controlling the tilt.
I found it easier to assemble the supports “sideways” initially with the bases clamped in the vice. The sides are each secured with two 2″ x No 8 screws inserted via the bottom of the base (not visible in my pics). The base of the Speakon brackets acted as a useful spacer when glueing the second side. I glued the sides, front elements and bracket bases together first, using wax discs again to keep the joints to the base glue-free so I could then unscrew the vertical assemblies from the bases to plane off any imperfections – planing options are limited once they are glued to the bases. Before gluing I had used a 12mm wood bore to lightly recess the front and rear fixing bolt holes on the bases.
After two coats of primer and some sanding and filling I found that the hinged elements were binding slightly on their lower edges when in their closed (vertical) position; this was easily solved by slackening and re-tightening the hinge screws which allow just enough play for fine adjustment.
The top of one of the small hardboard bolt retainers was a little proud so I took the plane to it – a bit too heavily, as it promptly snapped in two. They are fairly fragile. It too 10 minutes to mark out and cut a replacement, which fitted better than before, so nothing lost except a bit of dignity / pride!
The last week has seen the sometimes fiddly job of marking, cutting and drilling the baffle support parts. My new jig saw came in very useful here. We have a love-hate relationship; I never find it easy to cut accurately to a line with jigsaws, so experimented with running straight cuts using a guide batten clamped to the work – better, though still not reliable enough to cut really close. Leave a millimetre or so and plane therefore.
The first fiddly job was cutting the hinge rebates for the front tilt assembly. Birch ply is solid stuff! – so chisels were thoroughly sharpened first. One side was perfect first time; on the other the tilting upper part was a little out of line, requiring a few tho’ off to deepen the rebate at one end.
The other “learning experience” was setting in the threaded M6 brass inserts. My counterbore diameter was 10mm – the manufacturer specifies a hole between 10 and 10.8mm diameter so the inserts were tight. They are difficult to screw in accurately vertically and require regular adjusting heaves on the hex spanner to correct wander every turn or so. In the process there is a tendency for the outer plywood layer to lift and splinter, so I clamped scrap blocks either side after the first attempt. I then had to remove the inserts to widen the guide hole out to take the bolts before final insertion. Not all were perfect… but good enough.
The photos show all completed parts sitting dry on the base. The LX521 baffles have a striking angularity, so I decided to go with this and plane the front and sides of the bases to an angle also. I like the look! – quite racy. I will do the same to the front and sides of the top of the bridge.
The next job was to make some little brackets for the Speakon 8-way panel connectors; I didn’t have a 32mm wood bore so ordered a Bosch one from Amazon. It made a very neat job. I’m only gluing the horizontal component so I can remove the connector for wiring up – I don’t fancy digging around in what will be a black hole at the back of the support! The horizontal element will need careful positioning before gluing to ensure the bevel lines up with the support sides.
I still need to cut the front hardboard spacers together with the smaller oblongs that will be screwed to the back of the front assembly to act as a retainer for the adjusting bolt; they will have a hole just large enough for a hex screwdriver to engage with the bolt.
In the last week or so the boring work of priming, sanding and filling the woofer boxes has got under way, although the tedium is relieved from time to time by researching and ordering miscellaneous items from the internet. Chemical black bolts and self tapping screws of varying types from Accuscrews to mount the drive units and tweeter baffles, brass inserts and black flat topped bolts from Insert Co (UK) Ltd for the baffle brackets, a counterbore for the inserts, and finally Neutrik Speakon connectors (4-way for woofers, 8-way for the mid-range / tweeter baffles) from Canford.
The woofer boxes have now had their second full primer coat, and are looking good, if somewhat sinister. Wood grain is still visible, mainly where end grain is to be found, but they are feeling very smooth already. I’m leaving them at this stage to turn attention to the baffle bracket assemblies to which I have been giving considerable thought. The main question was how to build in tilt and toe-in facility without spoiling the overall appearance or involving unduly complicated engineering. My listening chair is quite low so I felt the tilt was essential, and from reading SL’s comments and related links I learned that being able to toe-in the baffles was important for not only minimising side and back wall reflections but also widening the stereo “sweet spot” (two or more listeners).
For tilt I finally opted for fitting a butt-hinge concealed just behind the bottom of the baffle, controlled by a fifth M6 recessed flat-headed bolt engaging in an extra brass insert positioned from the front of the hinged element. I’ll only need a few degrees of tilt so am hoping this will work.
This idea requires some modifications to SL’s basic design, principally the fitting of an additional fixed piece of 18mm ply behind the bracket front through which the adjuster bolt runs. In addition, I need to add a 3mm hardboard spacer behind the baffle for the twin purposes of ensuring (a) the baffle clears the hinge butt (I’m not digging holes in my nice cherry!) and (b) the bottom edge of the baffle won’t foul the front of the bracket when tilted. Finally I am adding a simple bracket inside the back of the support to mount the Speakon 8-way panel connector (6 will be used as with the Mini DSP option the lower and upper midrange units and tweeters are all driven separately).
Toe-in was more problematic. Pivoting the baffle support round a central bolt at the front of the support, vertically in line with the baffle, is easy enough; the problem was what to do at the back of the support. With the baffles tilted downwards I was concerned that the centre of gravity would be thrown forward sufficiently to make a rear bolt through to the bridge from the back of the support essential. I considered cutting a continuous radial slot in the bridge, but felt this would be impractical without a router. In the end I settled for drilling four additional holes, with brass inserts, in the bridge to give 10, 15, 20 and 25deg toe-in. If finer adjustment is needed (which I doubt) I’ll just lug the woofers around a bit…
Finally I ordered four veneered and edged cherry panels from SL Hardwoods for the sides of the bridges. The top and feet will be solid cherry; I have enough of the 7″ by 3/4″ cherry board (for the baffles; also from SL Hardwoods) left, though some jointing up will be required.