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BT-3000 Shim Supports



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December 3, 2000
I must be totally star-crossed this week . . .

"Trouble comes in threes," didn't someone say? This week I've already dinged the blades of my new planer, nearly dropped my router from the accessory table, and now this . . .

I thought I was immune to the shim problem. I knew about it, I was forewarned, I took precautions: I used a shop vac; I didn't exert excessive force (I thought) when raising and lowering the blade. I used spray Teflon lubricant and tried to keep the shims area clean. I've only had the saw for 8 months, and it hasn't been subjected to hard use.

But today it struck. Actually, several days ago I noted that raising the blade seemed to require just a bit of extra energy; I say "just a bit" because that is what it was; not a great deal at all. I didn't—and still don't— think I was applying excessive force. I removed the throat plate and glanced at the shims from the top; they looked normal and didn't appear dirty, but I blew them off with some compressed air anyway, sprayed a bit more Teflon on, and didn't give it too much more thought. But the minor resistance continued, and today it was beginning to trouble me, so I decided to look under the hood.

1. A bit of background for any newbies:
Two of the central parts of the BT3000 are the Locker Bracket and the Guide Holder (photos and schematic can be seen below). As the motor arbor is moved up and down to elevate the blade, the Guide Holder slides against the Locker Bracket. Since both these parts are made of relatively soft cast aluminum, direct contact and sliding would result in mutual wear and potential seizing. To prevent this kind of friction and damage, thin, oddly shaped stainless steel shims have been designed to fold around the edges of the Locker Bracket and slide between the two aluminum parts. Since these parts may be a bit unfamiliar to new users, Figure 1 below shows a schematic cross-section view of the parts involved.

(NOTE: The numbers designated with "#" in the illustration refer to the corresponding numbers on the parts diagram (Figure 59, page 40) of the Owner's Operating Manual. Also note that these schematics depict only one dimension of the shim; in fact, the shim is creased in the middle to fold around the corner of the locker bracket [see photo below]

Schematic Figure 1

Here's an actual photograph of one of the shims removed from the saw; note the way it's creased in the middle to fold around the locker bracket, and the little tabs folded over at the two ends:
Shims New

(IMPORTANT NOTE: The shim design has been changed on the new BT3100. See appended comment at BT3100 Shims below.)

Occasionally, however, a problem arises. It apparently happens—if it happens— when interference or excessive friction occurs in the path of the sliding shim, due to the collection of sawdust, other foreign matter, improperly adjusted shim set screws, or perhaps some other metaphysical cause (I personally think it has to do with the phase of the moon).

Based on the saw's construction, proximity to the main source of sawdust, and gravity, the most obvious place for foreign matter to collect is along the top edge of the shim. If interference causes the shim to become slightly stuck, the user will first notice it as a sensation of heavier-than-normal resistance when attempting to raise the blade. As the blade elevation handle forces the Guide Holder to rise against the stuck shim, the top edge of the Guide Holder begins riding over and bending the upper tab of the shim:
Shim Tab Bending

If the user continues to force the blade up despite the resistance, the Guide Holder will ride up over the tab of the stuck shim, flattening the tab and leaving the shim behind.
Shim Tab Bending

Finally, if the Guide Holder rises complete above the shim, the shim will fall out into the bottom of the saw. "Clink!"
Shim Tab Bending

. . . At any rate, once the tabs of the shim have been flattened in this way, loss of the shim is inevitable, even if it doesn't drop out immediately.

[Later note: Ryobi say that the shim set screws are supposed to be adjusted and applied with Loctite at the factory (instructions are here), so they normally shouldn't become loose or require readjusting. I wondered about mine when this shim problem occurred, so I took out the shim set screws and they indeed appeared to be applied with Loctite, so "working loose" doesn't seem to be an adequate reason for failure of the shim in my case.]

Okay now, the following photograph was taken six months ago, and is the way things looked when my saw was basically new; this is the way the shims should appear:

New Shims on BT3000
Shims, the Way They Ought to Look

The red arrows point to the rear-side shim, specifically, to the bent-over tabs that keep the shim from sliding down and out. While I haven't added any arrows, the front shim appears similarly on the right side of the photograph.

2. When I opened the cabinet today, though, I saw this: Tops of Broken Shims
Broken Shim Tops

Here, the top two arrows point to where the tabs of the rear shim should be, but aren't. In fact, when I first looked, the tops of the rear shim were nowhere to be seen; they had already been flattened and slipped down inside the Guide Holder. When I looked underneath, I could see the bottom of the shim extending well below the bottom of the Guide Holder, but it hadn't fallen out yet, so I placed my finger under the bottom of the shim and while holding it in place, I carefully lowered the blade elevation handle; eventually, the top of the shim emerged above the Guide Holder, but the tabs were flattened, and when I tried to gently bend one of tabs back down, it broke right off, resulting in the photo above.

3. I purchased my saw in the U.S., and even though it's only eight months old, Ryobi tells me that taking it out of the U.S. voided the guarantee. So I'm basically SOL; I assumed I'd have to order new shims and wait to put them in, but then I thought: there must be some way to modify the way the shims are held in place, to prevent their seizing and falling out.

Fundamentally, the shims are designed to slide easily, and as I noted above, one can hold them in place with just a finger underneath the Guide Holder while raising or lowering the blade arbor. The main problem seems to be there, at the bottom side of the Guide Holder: basically, the shim has nothing but its upper tabs to hold it in place and prevent it from slipping down, and those tabs apparently provide scant support when the shim meets resistance due to dirt, sawdust, or improperly adjusted set screws. Given the minor amount of additional force it took to bend the top shim tabs in my case, I consider this a design fault, one, however, which should be easily correctable with a simple shim support. As a result, I decided to add small L-shaped metal brackets which would attach to the side of the Guide Holder, bend underneath and act as supports to hold up and lift the lower shim tabs. (I should note that while only the rear shim of my saw has been broken, I decided to go ahead and make supports for both the front and rear shims.)

WARNING: I make no guarantees, express or implied, about the results of this operation. Don't try it if you feel at all hesitant about modifying your BT3K in a rather fundamental way. You may void your warranty by doing this, or cause serious functional damage to the saw.

4. I began by running to the local home center and buying a 4mm tap, a 3.3 mm drill, some 4mm machine-head metal screws, and a small strip of galvanized steel, 1.2 mm thick and 15 mm wide (the strip was about 100 mm long, which furnished enough material for two shim support brackets). These tools and parts cost me the equivalent of about four dollars, total.

5. I used vernier calipers to measure the distance between the outside surface of the Guide Holder (#80) to the face of the Locker Bracket (#10) which it slides against (the shims ride between these two parts). On my saw, the measurement was 11 mm. This is the distance the underarm of the new shim support had to reach.

Shim Support Bracket
Measure Carefully!

6. I first scribed a line about an inch or so from one of the finished ends of the galvanized metal strip. This one-inch part would form the mounting arm. I inserted the metal in a vise up to the line, and used a ball-peen hammer to bend the metal over to a 90° angle. I then used my calipers to carefully measure 11 mm from the bend, and there scribed another line across the metal. I used a hack saw to cut off the newly bent metal at the scribed line, then cleaned up the cut with a grinder and buffing wheel. By grinding the cut edge, I also assured the arm supporting the shim would be slightly less than 11 mm long, since I figured it should reach almost, but not quite, to the face of the Locker Bracket, to prevent it from touching and scraping the sliding face of the Bracket. I also estimated the one-inch (or so) length of the mounting arm so as to provide what I hoped to be sufficient clearance for the shim Set Screw (#73) that is also located here.

7. The galvanized metal strip came predrilled with a number of screw holes, and I opened one hole up a bit larger to accommodate a 4mm screw. The resulting support bracket now looked like the following photo: Shim Support Bracket
Shim Support Bracket

The red arrow points to the mounting arm and the direction the mounting screw will be inserted from. The hole in the lower support arm was one of the predrilled holes in the metal strip and is meaningless here.

8. Next, I marked the position of the mounting hole on the Guide Holder. As I noted above, I took some care when calculating this position and the length of the mounting arm, since there a shim Set Screw (#73) located nearby, and I obviously didn't want to interfere with that. I held the support in place and used a felt pen to mark the mounting hole's position. I then gently center-punched the spot, and drilled carefully using a 3.3 mm drill. The Guide Holder is not solid aluminum in this place, and the walls are not all that thick, so great care must be taken to prevent the drill from going too deeply through and striking the other side where the shim might be located (ideally, this operation should be done with the Guide Holder disassembled from the saw, so that you can see the other side of what you're drilling on. I didn't have time to disassemble the saw this time, so I discovered the thinness of the material as I drilled!).

After drilling the hole, I tapped it with a 4mm tap. Here is a photo of the newly tapped hole (arrow) for the front shim support, located just above the Set Screw hole:

Newly Tapped Hole for Shim Support Bracket

Newly Tapped Hole for Shim Support Bracket

9. Using a 4mm machine-head screw (8mm long), flat washer, and spring washer, I fastened the support bracket to the Guide Holder. Here is what the Guide Holder looked like with one support mounted:

Guide Holder with One Shim Support
Guide Holder with Shim Support

The left arrow above points to the newly installed rear shim support, while the right arrow points to the hole where the front shim support will be mounted next.

10. Finally, both shim supports mounted:

Guide Holder with Two Shim Supports
Two Shim Support Brackets Mounted

This photo is a bit dark, but the arrows point to the lower edge of each support bracket, where normally the bottom of the shims would emerge. These arms now support the bottom edges of the shim tabs, helping to lift the shims and prevent them from stopping when the Guide Holder rises; as a result, they should prevent the Guide Holder from running over and flattening the top tabs of the shims.

Once again, in order to clarify the parts involved, Figure 2 below is a cross section schematic showing the shim supports mounted. I only installed lower supports, but one could make upper ones as well to hold the shim in place during the downward movement of the arbor; I seriously doubt they are necessary, though, since it seems to be the top tabs that tend to get flattened in this way.

Schematic Figure 2

Aside from the run to the store, this entire operation took about an hour, and it should prevent any further damage to the shims. The new shim support brackets cover the lower shim Set Screws, but if any adjustment is needed there, the supports are easily removed. Needless to say, I can't guarantee anything about the process, and while it worked well for the rest of my work today, I don't know the long-term effects of the operation, and I don't recommend that anyone try it at all if they don't feel secure in the use of drills, taps, fairly precise measurements, and taking risks. Having said that, I've tapped very few holes before in my life, and these were two of the easiest to do.

Finally, if anyone decides to try the same thing, I would strongly emphasize the following points:

1. Be sure the horizontal arms of the shim supports aren't so long that they scrape against the surface of the Locker Bracket, since it could cause scoring of the bracket, further impairing the movement of the shims.

2. Be very careful when drilling near the shim Set Screws. Leave sufficient space between the Set Screw and the new hole, and drill slowly, to avoid going too deep and possibly striking the shims on the other side. Remember: these parts are aluminum. Don't apply excessive force when drilling, tapping, or tightening screws!

3. Be sure the screws you use aren't too long; they might also strike the shim on the opposite side of the Guide Holder!

4. These shim supports should help prevent the Guide Holder from running over and flattening the top shim tabs (i.e., when raising the blade); they will probably not have any effect on resistance encountered by the lower shim tabs, namely, the possibility of running over the lower shim tabs when lowering the blade. However, based on what I've heard from Ryobi and other users, it is the top area that presents the greatest potential for collection of resistance-causing foreign matter. (Which is to say, I've never heard of shims being ejected from the top of the guide holder!)

5. These shim supports should not be thought of as substitutes for properly tightened shim set screws. If you make these supports, be sure to check and adjust the tension of the set screws at the same time, reapplying Loctite as necessary. The following are Ryobi's instructions for adjusting the shim set screws as part of the procedure for replacing shims:

6. Before trying this, be sure you're serious enough about the desire for potential long-term relief to the shim problem that you're willing to void your warranty or otherwise destroy your BT3K!

IMPORTANT NOTE: The shim concept has been fundamentally revised on Ryobi's new BT3100 in order to avoid the problem of breaking shims. The old flat shims have now been replaced with "sprung" shims that appear as follows:
New BT3100 Shims
Ryobi say that these new shims can be retrofitted onto the BT3000, but only if you also replace the original BT3000 Guide Holder with the new one for the BT3100. That's certainly another option, but in consideration of the additional cost and labor involved in installing the new Guide Holder, it's got to be easier to install a pair of shim supports!

I should also note that if you don't want to drill holes in your BT3K, a variety of alternative methods of attachment exist. For one, check out these plastic shim supports

For more on the BT3100, see Sam Conder's Review of the BT3100.

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** Green Gables: A Contemplative Companion to Fujino Township
** by Norman Havens nhavens@gol.com
** Updated: January 1, 2004
** URL: http://www2.gol.com/users/nhavens/