Consistently Inconsistent Rear Alignment Problem

[Pichy]

I have drilled five blocks the same way, using a S.B. and a straight edge on the drill press. Been doing it this way for years with much success, but have occasionally had rear alignment problems. Tonight, I drilled the five blocks, then put good wheels and axles on them one at a time and did a slow roll test, with some weight. All axle holes are drilled 1/8" above bottom of car. Axles were pushed in but not as far as for a finished car. Just enough to be solid. In all five blocks, the rear right wheel will not migrate out to the head, but the left one does perfectly in both directions. I switched wheels and axles and tried different combinations. Same result. The fact that it so consistently happened to five blocks tells me that it is drilling technique, not wheels or axles. My drill press is very square to the table, tested with a dial indicator. Toothpicks inserted in the rear holes of all blocks "look" to be perfectly aligned when viewed from above, with same angle when viewed from the rear. What I haven't tried yet is using a bent axle on the DFW. I used a straight axle for the roll test. So I guess the front is riding a bit lower than it would if I had used a bent axle. I'll try that first thing tomorrow.

What else might be the problem?

 

[mxquad]

First, place the car with toothpicks on to graphing paper that has squares; this will show your alignment issue. Also, "maybe" when you flipped the car over to drill the other hole it's off a hair. We prefer to drill the rear axle holes at a -3 degree cant. Do you have the weight up 5 ozs?

 

[TRE]

Is your bit dull and walking.

 

[down4derby]

You can try marking a line down the center of the test block as well as the rear axle line. Drill a 1/4" hole at the intersecting lines then insert straight axles with point. This might reveal the problem.

 

[Pichy]

Some of the blocks were drilled with one drill bit, and then I bumped it with the S.B. and broke it, so I put in a new one and drilled the others. Weight was not up to 5 oz. I tried two different weights, but saw no difference. I can see light through the axle holes from side to side on all blocks. I'll try the 1/4" hole idea to see how the axle points align. I am using a 1/8" drill bit under the S.B. It is as long as the S.B. and very solid. Same diameter as the shorter pin that came with it. Maybe I should use the original pin? On all five, I put the blocks into the S.B. with the rear in first. I will try switching it and see what if anything it does differently to the new rear holes. I can't even begin to build the cars until I get past this. Gotta keep trying...

 

[Kinser Racing]

If your slow roll surface is not level, it would produce the same result.

 

[GravityX]

That's a good point. I fought the same sort of issue and solved it via leveling my tuning board, side to side. End to end it still sloped, as it should, a few degrees downhill.

 

[GravityX]

Another thought. I would also recommending sanding the bottom of the block flat to assure there is no slight crown, cup, twist or bow that is being straightened out when clamped into the SB. When released it will just revert back to into its old form and throw the drill off. Once you have lightly sanded the block flat (use a flat surface like a sheet of glass or surface plate, if available), then mount that newly flattened side towards the SB surface and clamp lightly, no need to squeeze the pine tar out of it.

 

[bracketracer]

Does the SB sit solid on that long drill bit? I'd be concerned that the long bit is sitting on a high spot somewhere along the table and throwing off the drill. Maybe try a shorter pin or drill bit centered under just the spot where you're drilling and see if it's better or worse?

 

[Kinser Racing]

A lot of very good drilling tips in this thread.

 

[BulldogRacing]

I had the same issues when I first started and the light bulb just went off with Kinsers suggestion. I bet my board was not side to side level at that time. Great tips, I agree. This is the foundation.

 

[Pichy]

Thanks for all the replies. The table was not level, but when leveled, the result was the same. I also had previously sanded the blocks on glass before clamping into the jig. This morning I drilled a new block with the original short pin instead of the longer drill bit under it. Again, the same result. Rear right won't migrate to axle head, though it does in reverse. I put a bent axle in the DFW to see if it would be different and it wasn't. I tried it on a track, and it did a little better with speed. The right rear pulled away from the car, but didn't go fully to the axle head. Seems that having the forward force helps a little. Then I switched axles over and over, and eventually got it to do exactly what it is supposed to do. That is, slow roll migration forward and backwards, as well as perfect track performance. So it must be that my axles are slightly bent, or slightly straight, or slightly something. This is a scout car, and everything is official BSA components. We can't deviate from that. As an experiment, I should buy a set of better axles just to see if it fixes things.

The fact that every time I drill, I end up with the same right wheel issue is unnerving. It's as if the SB is damaged (it is not- I have babied it from day one). Perhaps I should use a slightly thicker pin under the block? Would that make things even worse? Or would raising the DFW a little produce more toe out and better migration of the rears to the axle heads? I realize I need to keep trying everything...it's my issue to solve, and I will solve it one way or another. And thanks again for all the comments.

 

[bracketracer]

What are your corner weights looking like? Are they equal on both rears or is the left rear heavy?

 

[BulldogRacing]

when you test is your front wheel on the right every time? Try reversing the side to install the fdw and see if you get opposite results with rear wheel migration, with less then great wheels and axles this could be the case?

 

[B_Regal Racing]

For that test, you should have a straight axle installed in the DFW, with 3 to 4 oz of weight on the rear. I know its sounds obvious, but just eliminating variables...

 

[The Iceman]

I had the same problem, I have a large stand up drill press when I started and it drove me nuts!!! And it ended up being the base plate was cupped!!! I took it and had it turned for 30 bucks or so. ahhhhhhhhhhhhhhhhhhhhhh! lol

 

[Pichy]

My drill press is a craftsman, and my base plate isn't great. I bolted a piece of MDF to it, and then checked it for flatness. I put a runout gauge in the chuck and spun it by hand in a circle over the area where the SB will sit when drilling. It registered only .002 runout. I'll strip everything down after the scout race this weekend and start from square one, checking everything. I used a steel framing square as fence, bolted to the table. Maybe it's not square. I did not use a stop block on the end of the SB. Can this be the culprit, so many times in a row?

 

[pony express]

Problems in drilling holes can be multiple as you see. I had to switch chucks and that cured many things for me. The fact that one side is always off points to consistent drilling in your case. That might point to a problem with the silver bullet. Are their burrs along one side? Are the trough where the rod is placed not machined like the other side's trough. It's the area of the block where you place the sine bar. To check the error then I'd drill holes perfectly straight (no cant) and the compare. If it's the trough then your problem will disapear without the rod, but should always return with the bar drills. It's a good thing that you have consistent drills though. No chuck or drill bit problem.

 

[DerbyDad4Hire]

Just saw this. When I had this issue it was usually one of two things. Cupped or crowned press table or the pin not fitting in the channel the same. Try running a piece of 400 grit sandpaper through the channels and check for burrs. Get a piece of Scotch Brite and polish the Silver Bullet to make sure it is smooth. It is very easy for a slight ding to mess up your drill job. It only takes a slight variation to throw it off.

 

[pony express]

In isolating the problem you might try using pin gauges for the bar. One time I used the long rod method and found I had to use the same end of the rod to the same end of the silver bullit each time or I'd get funky results. It's safer to use the short pin gauges at both ends.