Author Topic: Another Comber / Coomber build  (Read 21017 times)

Offline Bluechip

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Re: Another Comber / Coomber build
« Reply #25 on: November 01, 2011, 07:06:27 PM »
I have a few modest talents. Knowing what I'm doing isn't one of them.

Offline saw

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Re: Another Comber / Coomber build
« Reply #26 on: November 01, 2011, 08:02:01 PM »
Thanks Bluechip I think I understand now  :doh:
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Offline Bernd

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Re: Another Comber / Coomber build
« Reply #27 on: November 02, 2011, 09:15:45 AM »
I cant figger out what spotting drills is, I have tryed Google translate but no  :doh:
I would like to find something that can help me centerdrill on the mill.  :scratch:

SAW,

Here's what they look like. LINKY

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Offline saw

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Re: Another Comber / Coomber build
« Reply #28 on: November 02, 2011, 09:30:43 AM »
Thanks, I have order one so I will know what you are talking about  :)
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Offline arnoldb

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Re: Another Comber / Coomber build
« Reply #29 on: November 02, 2011, 12:42:40 PM »
Thanks Gents  :beer: - and also for helping Benni out with the spotting drill stuff  :thumbup:

 :lol: I think I jinxed myself earlier in the build by mentioning I need to get spotting drills  :lol:.  They're not available locally, so I have to order from overseas, and right now the N$ is worth nothing, so I'll hang on a bit...  The spotting drills are not cheap!

No shop for me tonight; have to attend to domestic matters  :Doh:

 :beer:, Arnold

Offline DaveH

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Re: Another Comber / Coomber build
« Reply #30 on: November 04, 2011, 01:31:16 PM »
Arnold,

You can get them here in SA :D
 :beer:
DaveH
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Offline arnoldb

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Re: Another Comber / Coomber build
« Reply #31 on: November 05, 2011, 05:08:04 PM »
Thanks Dave  :headbang: - Aye - Somta makes them, but I nearly had a heart attack when I priced one for delivery here...  I love their tools.  In fact I exclusively buy their drills as they are reasonably priced and very good quality.  But the spotting drills are off the charts, along with their milling cutters.  I'd love to buy them, but economies of scale just does not allow it  :doh:  Have you found any others ? - I'd be happy to try them  :D


This afternoon I had a good solid 4 1/2 hours of shop time   :D

Started off on the base, and poked in the mounting holes for the columns:


I needed to mill a 2mm wide slot 6mm deep - and re-cutting chips is a problem, so I used a bit of wire to pipe in air from the compressor:


That slot would need 10 passes at 0.6mm deep per pass, so I dragged a chair closer and got comfortable.  The first pass nearly done:


And a little while later, all done without any drama:


Then I flipped the base, and countersunk the column mounting holes, and also drilled two 3.3mm holes 10mm deep to tap M4 for the mounting the base to wood later:


A trip to the bandsaw, and I got rid of some excess from the base:


And milled the rest down to size:


I thought I was done, then remembered I still needed holes to mount the cam to - those followed in short order - 2.5mm to tap M3:


When it came to tapping the holes, a problem raised its head - my taps are too short:


That's not the first time I've had this kind of problem with my M3 taps... So I diverted a bit and made a quickie tapping handle for such cases:


It works a treat  ;D - I just have to shorten the grub screw a bit:


I was thinking of making cast-iron bushes to press into the columns - to give good bearing properties combined with the brass that the cylinder block and shafts are made of.  Unfortunately I could not find any in a suitable size, and while I do have some 25mm CI I could turn down, that seems a bit of a waste for such an expensive commodity...  My next best choice was phosphor bronze, which I have quite a bit of and can get at a reasonable price, but research indicates that brass and bronze are "similar" metals and not good for bearings...  Well, I could use steel then; it would be better...  And then my eye fell on the 1m length of 17mm round PTFE I bought more than a year ago at a whim (and very good price).

Well...  Why not?... I don't see plastics used a lot on model engines, but it's supposed to be as slippery as snot, so should make good bushes for this application.  This engine will never be run on steam, so the issues with heat and water porosity shouldn't be a problem...  There are two problems though; a) Would it be acceptable to use a synthetic material in a model like this ? and b) I've never tried to machine PTFE  - not to any sort of accuracy anyway.

As to a) - It "feels" wrong, but then again, I wonder what the Verburgs, Duclosses and Spareys would have done; Some of their build specifications seem to use cutting edge materials in terms of what was available when they built their models, so I'm not going to feel too bad to add a bit of new technology...

And as to b) - Well, there's always a first time  :)

Decision made, I started; I just used my regular HSS tools that I use on everything; I just made sure all the cutting edges were honed sharp.  Cuts easily, though I had some chatter as I didn't add tailstock support right from the start, but even parting off is a breeze  ;D - small diameter bush done:


Bigger diameter bush in-making:


Both bushes were turned on the OD to a press fit in the columns.  I'm surprised; it was easy to accurately turn the plastic and get fairly acceptable finishes; I expected to struggle a bit with that, but it turned out rather well.  Pressing the inserts into the columns made a fairly significant change on the ID's of their bores. 
So I decided to try out my hand reamers on them; the 6mm one for the small shaft went well, and easily cut the bush ID to size again without any complaints.

The 12mm reamer was another matter; it wanted to chatter - severely...  I was trying dry cuts, so I decided to try a little lubrication... But what  :scratch:.  I settled on a squirt of the synthetic oil/water mixture I use when parting off steel; it worked a treat and the reamer smoothed right out and cut nice even chips out of the hole   :ddb:

For today's work, I ended with this lot:


I'm surprised by how well the PTFE bushes work  :D:
http://youtu.be/D8wbTMHXql8

The bush on the thin axle looks like cr@p though, so I think I'll make an aluminium insert to press in with a smaller bush that will be hidden by the flywheel hub later on.  I can make the ali insert nearly invisible and things should look nicer.
 :beer:, Arnold

Offline arnoldb

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Re: Another Comber / Coomber build
« Reply #32 on: November 06, 2011, 02:53:41 PM »
Today's four hour stint was done on the cam ring; it's not finished, but at least some progress.

I printed out the list of machining diameters  (Many Thanks goes to Gail Graham for making up the spreadsheet I used), jotted down some notes of things to keep in mind on it, and sawed a bit of 2mm brass plate from some stock I have:


The plate was smeared with some permanent marker ink, and laid out for the most important bits:


On to setting up for machining, and oh dear; it's too big for my rotary table:


But it will fit on the lathe's face plate if I mount that to the RT  :D:


I found a bit of wood off-cut  from last year's kitchen renovations, and mounted the workpiece to it with some self-tapping screws through the center bit where the screws will be inside the cutting tool path.  After that, I drilled holes through the corners where excess will be, but spaced to match up the face plate's slots when the workpiece is centered:


Mounted the face plate on the RT, and centered the RT on the mill as well as zeroing the X and Y handwheels - making an additional note on the cutting chart as to which direction I was moving the table when zeroing the handwheels:


Then I mounted the workpiece on the face plate, lightly tapping it till I could get it as centered as possible.  The mill's X and Y wheels were left strictly alone on zero.  The idea is to center the workpiece to the center of the RT here:

I also tried to get the base reference as parallel to the X travel of the mill as possible by eye.

Once I was happy that the workpiece was centered, I cranked on X to check on the rotational orientation:

I'd eyeballed the rotation to less than half a degree, so I cranked the RT to bring the line on center and zeroed its dial.

One disadvantage of having screw-on chucks/faceplates is in a scenario like this.  In this case, the face plate screwed on with it's slots offset by about 30 degrees, so I couldn't use the RT's own degree scale:


Oh well, a permanent pen can make a new scale; I'm going to work without any cutting fluid, so the markings won't be washed off:


Next I bodged up a DRO - One day I'll get proper DRO's but for the most part I don't mind reading the handwheels:

 :lol: - I did say "bodged up"   :lol:

A final check of everything later, then a cup of coffee, pulled up a chair, and started...  I'd calculated the cutting path for a 12mm cutter, so I drilled a 10mm hole to start things at the first coordinate after locking both X and Y axes on the mill and the RT's table.  The hole is to give the cutter less material to cut away for a start - and prevent things moving:


Then I started with the 12mm cutter - same location and drill it out to size, mark the first coordinates on the sheet done.  Then the roundabout began... Unlock RT, feed 2 degrees, lock, unlock X, dial in the new coordinate, lock, drill new location, mark as done on the sheet.  Repeat.  About 60 degrees later:


I stopped for the day at 178 degrees:


It takes about 45 minutes to do 90 degrees and a LOT of concentration (maybe I'm just a slow worker  :lol:).  One mistake, and I'll get to start all over   :coffee:  And it is a bit of a mind-numbing process, so better to carry on when I'm fresh.  That's why I put a new battery in the caliper; so it can "remember" the last reading, and why I meticulously marked off each position as it was done and the state of the mill when I started; at least I can stop and pick up from there later.

 :beer:, Arnold

Offline arnoldb

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Re: Another Comber / Coomber build
« Reply #33 on: November 13, 2011, 11:16:11 AM »
After a hectic work week and most of my weekend spent on getting an additional data center going for my company I finally got some shop this afternoon.

Finished off the last 180 degrees of the cam:


Drilled the two 3mm mounting holes:


I nearly forgot to clamp down the outer bit to the wood block before removing the bolts holding everything to the face plate...  Fortunately I realised just in time and added a couple of screws through the mounting holes to keep it in place.  The whole lot needed to be moved on the face plate to the outer ring center to finish things off, and if it moved it would have lost its place on the center piece that has the center position marked! :


Of course, last weekend in a blinding flash of idiocy I didn't drill additional mounting holes offset with the required 8mm from the initial ones, so no mounting holes could align with the face plate slots once I moved the workpiece to the new center   :lol: - So I grew a forest of clamps to finish the rest of the machining operations:


That meant I had to stop during machining to move clamps around to get out of the way - here is one of the stoppages to move a clamp:


Finally - all machining done on the cam three hours into the shop session:

Not a miss-step or anything, and that's the hardest part of this build done   :ddb: - just some clean-up left to do.

A close-up of the cusps left by the machining process on the inside of the cam:


They look worse than they are; a little very light and careful filing with a 250mm fine half-round file brought the roughness down very quickly till all the cusps were barely visible and even in size right around the ring.  Then I wrapped some 320 emery around a bit of 50mm pipe, and in careful circular motions around the ring removed the last visible signs of the cusps.  All this was done very carefully; things needed to just be smoothed out; the shape mustn't change.

After a bit of file work around the outside of the ring to get rid of tool marks, and a rub over some emery and a quick rub with scotch-brite to give a brushed finish, the cam is done:


What do you know? - things fit together and is starting to look like an engine:


That's the engine half-way done then; so only 90% to go   :)

 :beer:, Arnold

Online sbwhart

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Re: Another Comber / Coomber build
« Reply #34 on: November 13, 2011, 12:37:48 PM »
That cam ring realy look the buisness, cracking bit of machining Arnold.

 :clap: :clap: :clap: :clap: :clap: :clap:

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Offline saw

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Re: Another Comber / Coomber build
« Reply #35 on: November 13, 2011, 01:59:39 PM »
Fine as usual, but I have to ask  scotch-brite what is that? :doh:
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Offline Bluechip

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Re: Another Comber / Coomber build
« Reply #36 on: November 13, 2011, 02:13:08 PM »
Benni

Abrasive pad, similar to this ...


http://www.arceurotrade.co.uk/Catalogue/Abrasives/Hand-Pads

Cheaper than genuine Scotchbrite, but just as good for most things ,,

BC
I have a few modest talents. Knowing what I'm doing isn't one of them.

Offline Kjelle

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Re: Another Comber / Coomber build
« Reply #37 on: November 13, 2011, 02:28:23 PM »
Fine as usual, but I have to ask  scotch-brite what is that? :doh:

Hi Benni!

Dom där gröna disksvamparna, du vet...

Kjelle

Offline saw

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Re: Another Comber / Coomber build
« Reply #38 on: November 13, 2011, 03:03:43 PM »
Thanks everyone  :clap:
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Offline Brass_Machine

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Re: Another Comber / Coomber build
« Reply #39 on: November 13, 2011, 11:33:39 PM »
Another one that I missed.

Excellent work!

Eric
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Offline Stilldrillin

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Re: Another Comber / Coomber build
« Reply #40 on: November 14, 2011, 02:18:12 AM »
Fine work done well, Arnold!  :clap: :clap: :thumbup:

David D
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Offline Doc

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Re: Another Comber / Coomber build
« Reply #41 on: November 14, 2011, 10:46:00 AM »
Looking good Arnold. The cam ring looks nice I have to laugh at your comment 50% done only 90% to go.
 That's how I feel some time during a build.
Keep up the good work!
George

Offline arnoldb

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Re: Another Comber / Coomber build
« Reply #42 on: November 15, 2011, 12:51:00 PM »
Stew, Benni, BC, Kjelle, Eric, David & George - Thanks for checking in Gents   :beer:

Benni, like BC said - scouring pads  :thumbup:.  The ones I use are the green ones available in grocery shops for scrubbing post & pans in the kitchen.  I tried some other brands that's available on the shelves, but the genuine 3M Scotchbrite sold in the kitchen section works best for me; I use a lot of them; half in the shop and the rest for scrubbing pots that burned on while I'm posting  :D  :lol:

George, glad you had a laugh; the 50% done and 90% to go seems to be a sort of a fact while building engines.  For me, that's mostly because I tend to start with the easiest-to-make parts, which are normally the biggest.  The hardest part of any build is in the handful of small bits; they take more time and setup to make, and trying to get a good finish on those are the hardest.  All good fun though  :D

I stole an hour in the shop after work today; decided I'll fix up one of the eye-sores...

I removed the big ugly PTFE bushing from the "thin-shaft-side" bearing column, and turned up an aluminium filler piece and smaller PTFE bush, all for press fits:

The PTFE bush I did twice; on the first attempt I turned it's OD 0.02mm under the size needed, and that resulted in too light a fit...

The aluminium insert pressed into the big hole:


After a bit of filing and emery, the joint is nearly invisible:

You can click the photo above to see a bigger version; there it's more visible.

New bush pressed in - intentionally standing 0.5mm proud on either side of the bearing column:


That looks a lot better; in fact, once the flywheel is mounted, the plastic bush will be nearly hidden:


 :beer:, Arnold

Offline cfellows

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Re: Another Comber / Coomber build
« Reply #43 on: November 17, 2011, 10:50:14 AM »
Coming together very nicely, Arnold. 

Chuck

Offline saw

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Re: Another Comber / Coomber build
« Reply #44 on: November 17, 2011, 12:58:17 PM »
Nice build, when this engine is finish there is a small chance that I understand this engine  :lol:
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Re: Another Comber / Coomber build
« Reply #45 on: November 18, 2011, 04:12:43 PM »
Hi Arnold  :clap: :clap: :clap: :clap:


Well done mate ,,,,,,,cam ring came out great  :bow: :bow:

Rob  :D

Offline DaveH

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Re: Another Comber / Coomber build
« Reply #46 on: November 19, 2011, 01:58:38 PM »
Arnold,

Coming along great :thumbup: :clap:
 :beer:
DaveH
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Offline arnoldb

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Re: Another Comber / Coomber build
« Reply #47 on: November 19, 2011, 07:49:49 PM »
Chuck, Benni, Rob & Dave, thanks for checking in Gents  :beer:

Benni , it's starting to come together now  :thumbup: - Just ask if you want to have more detail; I'm happy to try and help  :D   :thumbup:


Today's bit; I had a good shop session, so lots of photos...

I started work on the piston.  Earlier in the build, I left the bore of the cylinder just a tad under the 16mm I wanted.  That was on purpose; I have some 16mm round brass bar to make the piston from, but it needs a bit of skimming, so will end up under 16mm.  I chucked the brass bar up in the collet chuck on the lathe, and faced it and then parted it down part-way on 5mm length:

Starting with a partial parting cut might seem silly, but there's a reason for it.  If you look closely at the above photo, you'll see the burrs raised on both sides of the parting cut.  If I left this for last, that would leave a ridge on the piston that I'd have to remove in some or other fashion - and there's no easy or accurate way.

A little later, and I'd used a small file to put chamfers on both sides of the piston, a free-hand oil groove with a triangular needle file, then turned it to final size and drilled it 2mm through the center:


After finishing the parting cut, I ended up with this:

The face shown is on the parted-off side; I still need to practice parting a lot more to get better finishes.  The pronounced countersink on the hole was added manually; on both sides of the piston; these are needed for later steps.

Next I started on the forks.  Drilled a 1.6mm hole through some 6mm thick square brass:


Then I mounted the slitting saw on the mill and used my height gauge to pick up the top of the block and set the slitting saw to height:


I just used my 0.5mm slitting saw to slit through for the fork bodies deep enough to later cut them off.  Then added my 1mm slitting saw to the arbour to start cutting the forks - using the height gauge again - this left a 1.5mm wide slot; which I just slit to depth on the line I'd marked:


I then moved the mill quill down by 1mm, and slit again - leaving a 2.5mm wide slot, and then moved down and repeated:

If you look carefully, you'll see there's two stilling saws ganged together; a 1mm and a 0.5mm one.  I really need to buy more slitting saws :big:

The block was then flipped in the vise and clamped down with a generous bit of cardboard to prevent things moving, and then the two forks slit off from the parent stock:


I then drilled the backs of the workpieces 1.6mm to tap M2 later:


After tapping and then some free-hand filing to round over the ends, the forks were done:


I needed some bolts to hold the cam to the base.  Any old 3mm screw would have done, but I rather made my own. Here's some 5mm hex brass turned down and threaded with the tailstock die holder:


After some more machining, I had these:


The cylinder block needed some holes plugged - just two bits of 2mm brazing rod plugged in with high-strength retaining compound:

Ugly, innit ?  ;D

Some more 2mm brazing rod followed to make the connecting rod; threaded both ends M2 to fit the forks and lock nuts.  The piston have to be soldered on in the middle:


I used some aluminium drinks-can plate to clamp down the connecting rod with the piston in place.  The plate keeps the piston on the correct height and prevents the vise from marring the connecting rod.  Any solder that leaks through won't stick to the aluminium plate either:


Some soft-solder flux was brushed on before assembly, then I soldered the lot together with some electronics solder. I just used a small plumber's blow-torch to heat things up.  It looks horrible here, but worked quite well:

Remember the chamfers I mentioned on the piston earlier on? - This is where they came into play; I made the hole in the piston a relatively tight fit to the connecting rod, but they had to be soldered together, and with the hole being tight the solder would not flow through.  The chamfers provide the necessary area for the solder to make a reasonable secure joint.

Next I cleaned up some 6mm silver steel rod and drilled it through and reamed to 4mm, and parted off two rings 2.4mm thick:


Some brass followed, a tad under 4mm OD for a smooth running fit in the silver steel above, and parted off at 2.5mm lengths:


Makes for some OK bearings:


A quick trial-fit in the cam, and I could see how much to adjust the forks in the connecting rod:


All assembled together:

Please excuse all the oily marks and so on; when I assemble something for the first time, I use a LOT of oil.  As can be seen from the photo, I''d also filed down and smoothed over the plugs on the air passages to blend in to the main shaft

There was a couple of tight spots on the cam with things all assembled; that was easily taken care of with some light filing and emery paper.
Things turned over fairly smoothly after that by hand, but wouldn't give me the easy flick with multiple rotations... and I was NOT happy; I'd built this engine so far to be EASY to run!
It was supposed to spin like a top...

At this point Thor threw a hammer at me noggin, and connected... HARD... ; Well, DUHHH - I've not yet drilled the main bearing column for an  air supply or exhaust...  - There is nowhere for the cylinder to suck or vent...  So obviously it would not run well  LOL - It needs a bit of breathing  LOL

Regards, Arnold
« Last Edit: November 20, 2011, 12:20:30 AM by arnoldb »

Offline Stilldrillin

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Re: Another Comber / Coomber build
« Reply #48 on: November 20, 2011, 02:32:22 AM »
Nicely done, and shown Arnold!  :clap: :clap:

Hope it's soon spinning free..... It's always a nice moment, when you hear an engine start breathing........ :thumbup:

David D
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Still modifying bits of metal... Occasionally, making an improvement!

Offline arnoldb

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Re: Another Comber / Coomber build
« Reply #49 on: November 20, 2011, 02:05:05 PM »
Thanks David  :D - I agree; that first time an engine starts is always the best :D

I didn't get a lot done today, but had quite a bit of fun   :ddb:

First I drilled the column for the port holes - just 2.5mm straight through the center through both sides.  One side will be tapped M3 for the airline connection, and I used a 6mm end mill to make a flat for the connector to screw up to:


Then I turned up the airline connector from some 6mm hex brass:


And then the real fun started; everything except the flywheel was there to give the engine a test run - so I tried it   :dremel::
<a href="http://www.youtube.com/watch?v=jHJ0YAyGoA4" target="_blank">http://www.youtube.com/watch?v=jHJ0YAyGoA4</a>

 :ddb: :ddb: :ddb: :ddb: - I didn't even know if it would run after all the changes I made.

I borrowed the flywheel off my grasshopper engine, and added that; after about 10 minutes of running, it could do slow too:
<a href="http://www.youtube.com/watch?v=gSra3sXZQoE" target="_blank">http://www.youtube.com/watch?v=gSra3sXZQoE</a>


It's not quite running on breath power; an almighty blow gets me a couple of turns, but I think I can get it running as I want with a slightly bigger diameter flywheel with most of the weight in the rim and some additional run-in time. 

So, it's flywheel, wooden base and final cleanup to go now...

 :beer:, Arnold