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Author Topic: Preac Table Saw Restoration  (Read 1441 times)
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« on: May 09, 2019, 12:35:37 PM »

One of the first tasks in setting up my modelling workbench again was to restore my Preac Miniature Table Saw. Unfortunately during the time our belongings were in storage prior to our move to Canada, corrosion developed on the Preac table as you can see in the first photo. The Preac saw is an excellent tool. I've owned mine since the early 90s and it always performed flawlessly. If you ever have the opportunity to pick one up, I recommend it.

Opting to address the issue myself, rather than have the table re-machined, I used electrolysis to remove the rust. The process is very simple. You need a plastic bucket, a tin can large enough to completely surround the rusted object, a battery charger set to 2 amp output, some stout solid copper conductor wire,  and a solution of water and baking soda. Remove any labels and the bottom from the tin can and solidly attach a length of copper wire to it long enough to connect the positive lead from the battery charger, on the outside the bucket. The tin can is the sacrificial anode. Next clean the rusted object to remove any oil, wax or dirt, and solidly attach a second copper wire to the rusted object, again long enough to connect to the negative lead from the charger, on the outside of the bucket. Place the tin can in the bucket and suspend the rusted object in the centre of the can so it is completely surrounded by and not touching the can. Then add sufficient water to the bucket so that the can and tool are completely covered then add and mix in the baking soda at the rate of 1 tablespoon per gallon of water. Double check your setup to be certain the rusted object is not touching the can, then, with the charger unplugged, connect the positive lead to the wire attached to the can and the negative lead to the wire attached to the rusted object. The polarity is very important. If reversed, the rusted object will become the sacrificial anode. Set the charger at the 2 amp setting and plug it in. Within a minute you should see bubbles rising from the rusted object. Let it run for 12 or more hours, depending on how much rust there is, until you see a disgusting looking rust and black sludge on the top of the water. You can see my setup in the second photo, picture taken just after starting the charger.

Continued in Part 2...


* PreacTableNastySm.jpg (195.24 KB, 550x411 - viewed 59 times.)

* PreacElectrolysisSm.jpg (177.4 KB, 550x411 - viewed 59 times.)
« Last Edit: May 09, 2019, 04:35:54 PM by finescalerr » Logged

Paul

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« Reply #1 on: May 09, 2019, 12:39:09 PM »

Once the electrolysis process was complete, I removed the Preac table from the bucket and cleaned it thoroughly under running water to remove all the sludge residue. You can see the result at this stage in the first photo, still a little nasty looking but the rust is gone.



The final process in the table restoration was the most tedious, involving lapping the table using emery cloth on a surface plate. You can see the end result in the second photo. Yes, there is some pitting from the corrosion (which could be removed if you wanted to spend hours and hours lapping) but, as it is merely a visual flaw with no detrimental effect on the function of the saw, i chose to leave it at this state. As it happens, most of the work I do with saw utilizes a table saw sled I made years ago (believe I made a post about that here but I can no longer find it), so the surface of the table is generally hidden from view. Given the polished surface, the sled slides freely which is the most important consideration.



Next step is to fully reassemble the saw and in the next posts I'll show what can be done with this excellent tool using the sled.


* PreacTableLessNastySm.jpg (189.3 KB, 550x411 - viewed 57 times.)

* PreacTableRestoredSm.jpg (181.87 KB, 550x411 - viewed 60 times.)
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Paul

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« Reply #2 on: May 09, 2019, 02:17:22 PM »

Saw is now completely reassembled, lubed and running beautifully. Picture shows the sled in place. Base of sled is 1/16" thick aluminum, bead-blasted on top surface to prevent stock slippage and polished on the underside to promote sliding on the table. Support rails are 3/8" square steel. On the underside is a 1/2" wide brass strip which locates and slides in the channel machined in the Preac's table. The blade in the photo is a 2" dia. x .051" T. slitting saw blade. One of the best features of the Preac, apart from its precision, robust construction and absence of plastic, is the ability to use slitting saws of various thickness. I have blades ranging from .016" - .051" T. which can be used for either wood or thin metal stock, taking full advantage of the precision built into the saw.


* PreacAssembledSm.jpg (222.01 KB, 575x430 - viewed 65 times.)
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Paul

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« Reply #3 on: May 10, 2019, 09:32:22 AM »

A little Preac madness - 1:48 pseudo-shiplap siding stock. About 25 years ago, Richard Christ and I produced a limited-edition craftsman kit called Clyde's Place, a depression-era road house derived from original photos in the Library of Congress. It was board-by-board construction with full framing (based on construction practices of the time), sheathed in shiplap siding. All the framing pieces were cut to size on our Preacs. We cut approx. 30 metres of shiplap siding stock, ripping the edge rebates on our Preacs using a .025" thick slitting saw set to a cutting depth of .012", midpoint of the siding stock. We kept the stock flush to the table using a small piece of scrap wood which we held in place over the saw blade with our fingers. I have fond memories of several days sitting in Richard's back yard, cutting stock for the kit while on a week-long trip to CA, back in the day when you could pack a miniature table saw in your carry-on bag!


* ShiplapPreacSm.jpg (196.05 KB, 550x411 - viewed 56 times.)
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« Reply #4 on: May 10, 2019, 12:37:09 PM »

Using the sled with the Preac saw, it's possible to make precise repetitive cuts and some basic joints in scale lumber. Cutting multiple pieces to the same precise length is very simple. All you need do is attach a small clamp to the lower rail on the sled at the desired length (photo 1). The length is measured between the inside edge of the clamp and the facing edge of the saw blade. As always make a test cut to determine that you have the length set correctly. If not adjust the clamp position as required. When correct, simply feed stock up to the edge of the clamp and cut, producing identical lengths of stock.


* PreacSledSetupSm.jpg (187.75 KB, 550x411 - viewed 56 times.)

* PreacRepCuttingSm.jpg (182.82 KB, 550x411 - viewed 57 times.)
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Paul

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« Reply #5 on: May 10, 2019, 12:47:25 PM »

I remember Richard's showing me some of that siding, then running a strip of wood through his Preac to show how he did it. I also remember visiting you and seeing an On2 diorama layout you were working on. -- Russ
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« Reply #6 on: May 10, 2019, 01:12:05 PM »

Yep... years ago when we were all much younger and not the grumpy old men we are now...  Grin Grin Grin

Unfortunately, I had to scrap the On2 Wiscasset diorama before we left for Canada. It had been stored in its crates in our storage unit and suffered moisture damage to the point that almost the entire surface was covered with mold. The black death had come to Wiscasset! I was able to salvage the turntable which was unaffected and most of the hardware, then cut up and trashed the rest... depressing job.  Cry
« Last Edit: May 10, 2019, 01:33:26 PM by WP Rayner » Logged

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« Reply #7 on: May 10, 2019, 01:12:42 PM »

Because of the Preac's precision, it is possible to cut accurate simple joints in scale lumber. In this post I'll go over the basic half-lap joint. You may ask why go to this trouble. The answer is simple, for the same reason that such joints are used in proper timber construction: strength of the joint and accuracy of the structure. Most scale wood models are glued together, very frequently with butt joints, i.e. the end of one piece of wood is glued to one of the surface of another piece of wood. This method will ultimately fail for the simple reason that end grain has no glue strength. In a butt joint, the grain structure of wood will actually wick glue away from the end grain. The answer is to provide two face surfaces which can be bonded together for maximum strength. Now, admittedly it may not be necessary to do this on very small components, but if you're building a large timber structure, i.e. trestle, it's well worth the effort.

Setting up the saw to cut a simple 90 or 180 degree half-lap joint is fairly simple, requiring accurate measurements and adjustment of the cutting depth. For the 90 degree joint in the photo below, I set up the clamp stop on the sled rail to the width of the stock (measured from the inside edge of the clamp to the opposite face of the slitting saw blade). Then, using the depth micrometer (blurry object standing the background on the sled) I set the cutting depth of the blade, in this case .040", halfway through the .080" T. stock. Then I made a test cut to be certain both the distance and depth were correct. Once correct it was simply a matter of making the initial cut with the stock pressed up against the clamp, then repetitive cuts to remove the balance of material between the initial cut and the end of the piece of stock. Same process was repeated on the second piece. Once assembled, you have a perfectly square 90 degree half lap joint between the two pieces of stock which when glued together will produce a very strong structural joint. Admittedly this adds time to the construction process, but once you've done it a few times, you can actually complete the process quite quickly.

In the next post, I'll show how to use the sled to make repetitive angular cuts (not 90 degrees) with accuracy.


* HalfLapSm.jpg (162.2 KB, 550x411 - viewed 55 times.)
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« Reply #8 on: May 10, 2019, 02:32:37 PM »

     As with any iron or steel machine table top, a regular waxing with a good floor WAX (not polish) will help keep the rust at bay.  I am currently using a 1 pound tin of Minwax clear wax and it will last for years.  If the wax dries out, add a slug of Naphtha and seal tight for a day or two.

     For a saw as small as this one store it in a heavy plastic bag with a handfull of silica gel packets.  I recycle mine from the local Walmart where I collect them from around the picture frames they sell.  About once a year simply put all of them on a cookie tray and have them spend the night in the oven at a temp of 220 degrees F and they will be recharged.  The clerks at my local don't care as they regularly throw them out so my getting them isn't a problem.

     Slitting saws can be purchased from Victor Machinery: https://www.victornet.com/ I deal with them for many things and am a happy customer and not connected to them in any way.
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« Reply #9 on: May 10, 2019, 02:38:33 PM »

Nice job of saving the saw Paul. Although spendy at the time these are great little saws for fine work. I bought Mine in Maine when they first came out. I carted it back and forth from Maine to Eugene, Oregon several times. I used it in teaching classes in miniatures. The only complaint was the inline switch on the power cord. Because of students using the saw I designed a quick shut off using a rocker type light switch. Start it by pushing the switch through the hole.  a light tap on the board stops the saw. The little green thing is a scientific scissor jack used to fine adjust the saw height. Shown are some fine frames sawn from beech for mounting beveled glass for a model popcorn wagon. Hope you post more on using the saw.

Bill


* saw - 1.jpg (48.54 KB, 432x324 - viewed 61 times.)

* saw - 1 (2).jpg (76.45 KB, 500x468 - viewed 68 times.)

* saw - 1 (1).jpg (80.14 KB, 459x466 - viewed 59 times.)
« Last Edit: May 10, 2019, 02:40:50 PM by 5thwheel » Logged

Bill Hudson
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« Reply #10 on: May 10, 2019, 06:04:49 PM »

     As with any iron or steel machine table top, a regular waxing with a good floor WAX (not polish) will help keep the rust at bay.  I am currently using a 1 pound tin of Minwax clear wax and it will last for years.  If the wax dries out, add a slug of Naphtha and seal tight for a day or two.

     For a saw as small as this one store it in a heavy plastic bag with a handfull of silica gel packets.  I recycle mine from the local Walmart where I collect them from around the picture frames they sell.  About once a year simply put all of them on a cookie tray and have them spend the night in the oven at a temp of 220 degrees F and they will be recharged.  The clerks at my local don't care as they regularly throw them out so my getting them isn't a problem.

     Slitting saws can be purchased from Victor Machinery: https://www.victornet.com/ I deal with them for many things and am a happy customer and not connected to them in any way.

Thanks for bringing up the wax Lawton. I meant to include the same tip, something I was taught years ago at furniture design school, but forgot all about it when writing the post. I've always used hard carnauba wax for the purpose which is how we were trained at school. Every Friday afternoon it was tools down and machine maintenance time, during which we waxed all the steel tables in the workshop. Unfortunately, I didn't wax the Preac table before I packed it up for storage in plastic. I believe there was enough temperature fluctuation during storage that condensation formed on the table leading to rust. I had a few other tools suffer the same fate but not nearly to the extent of the saw. I too now use the silica gel packets in all my tool drawers, cabinets, and chests which is a very simple way to control moisture in the enclosed environment.

Thanks for posting the link to Victor Machinery. I purchased all my slitting saws and most of my milling and lathe cutters from MSC Industrial Supply: https://www.mscdirect.com/.
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« Reply #11 on: May 10, 2019, 06:19:05 PM »

Nice job of saving the saw Paul. Although spendy at the time these are great little saws for fine work. I bought Mine in Maine when they first came out. I carted it back and forth from Maine to Eugene, Oregon several times. I used it in teaching classes in miniatures. The only complaint was the inline switch on the power cord. Because of students using the saw I designed a quick shut off using a rocker type light switch. Start it by pushing the switch through the hole.  a light tap on the board stops the saw. The little green thing is a scientific scissor jack used to fine adjust the saw height. Shown are some fine frames sawn from beech for mounting beveled glass for a model popcorn wagon. Hope you post more on using the saw.

Bill

Thanks Bill... beautiful work on the beech frames! My Preac came with a toggle switch behind the motor rather than an inline switch on the power cord, which I can see being not only awkward but a safety issue as well. I really like your little scissor jack, that's pretty slick. I made a slight modification to the saw which does essentially the same thing, drilling and tapping a hole in the pivoting plate that holds the blade shaft bearings and adding a socket head cap screw, the end of which bears against the underside of the table. This works fine for raising the blade to the desired height, then locking it in place with the stock clamping screws.
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« Reply #12 on: May 10, 2019, 10:58:09 PM »

     When I was at what is now Pittsburg State University in South East Kansas in the 1970's we ended every lab with a waxing of the machines in the shops.  When I ran a cabinet shop, it was also done daily.  Now I start and finish each work session with wax (at the end first vacuum machinery).  Even aluminum tool surfaces such as the newer Chinese made joiners and planers work better with a coat of wax.  My larger (read professional) machinery is covered with a cheap blanket and then a plastic shower curtain when I leave the shop.  In the winter each machine has a low wattage lightbulb placed inside of the machine to keep it above the dew point so that condensation isn't a problem.  I feel I'm always fighting rust which isn't really a bad thing because it forces cleanliness.
     As for the demo of the siding you created.  It isn't a pseudo-siding, it is the real thing, just in miniature.  Scribed sheet stock representing shiplap is pseudo-siding. 
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« Reply #13 on: May 11, 2019, 07:20:10 AM »

Thanks Lawton for pointing out that our siding was real ship lap, just in miniature. Yes, fighting humidity is a constant challenge, especially here in the east. Much more of a challenge than it was when we lived in California. Thinking back on it, we packed and moved everything into storage in early winter, which where we were in CA, meant damp and foggy weather. If I'd taken more care packing the Preac, like I did with the lathes and mill which didn't suffer any corrosion, I suspect I wouldn't have had the corrosion problem on the saw. At any rate, it's all good now.

Yes, the importance of machine maintenance and cleanliness was beaten into us repeatedly at the school and workshop (Wendell Castle School & Studio). We used to say a clean machine is a happy machine...  Wink  Your solution of a low-wattage lightbulb during winter months is brilliant, a simple and effective solution.
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« Reply #14 on: May 11, 2019, 11:22:02 AM »

The lightbulb is the poor man's choice to provide a little heat to keep the moisture out.  The Navy Shipyard in Norfolk uses what they call heater bars inside of motors which they wrap in insulation and plastic to keep moisture out onboard the mothballed ships.  Simply a case of monkey see, monkey do.
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