SB Pro - Help

HAB

Pinewood Ninja
Feb 16, 2017
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I need a pointer or two..............I received my SB Pro and good #44 bit from DD4H and drilled a car. The underside of the 5/16" thick car is hollowed out and was a really tight fit in the SB. I didn't have pin gauges at the time and I wanted to build some Bulldog fenders for it so I didn't verify the holes (Won't do that again). After I got the fenders built and attached I put it weighted on the test board and noticed that the rear tires were not migrating out going forward. They did migrate out when pulled back, and the car didn't stay straight when pulled back. After putting a square on it the 3 degree angles are correct but both axles lean toward the front of the car instead of being perpendicular with the body.

I drilled my son's solid body car (it was a snug fit) and the alignment checks out with the square, the wheels migrate out (although one is quicker and migrates farther than the other) both forwards and backwards on the board, however, it still does not track backwards in a straight line.

Since I screwed up the first hollow body car and couldn't redrill it with the SB as the fenders are attached I made a second car (plus it was a chance to play with a router bit in my drill press using the cross slide vice I recently purchased). After routing the body I put the car into the SB Pro and again it was a super tight fit. The 3 degree angles were good, the rear tires migrate outward (one faster than the other) in both directions, but it doesn't stay straight when pulled backwards. Using a square and pin gauges it looks like one side is leaning slightly forward toward the nose of the car.

How tight should the cars fit into the SB Pro? I wonder if the hollow body car is flexing when squeezed into the jig.

On the video 5Kids made using the square and thumb tack his car always stayed straight in reverse. What is causing my cars not to track straight going backwards?

What is causing the holes to have a forward (toward the nose) angle? Its not the SB Pro, maybe the drill bit is wandering? Any suggestions on correct drill technique?
 
My first thought was that you need to sand your body so it fits better into the SB Pro... I think you may be flexing the thin hollowed body because it is so tight in the SB Pro. You body doesn't have to be tight at all in the SB Pro, it just has to stay in one place.... if it is a little loose clamp it.

The video you referenced is Lightning Boy's or Bulldog's... i think... not mine, but i would like to take credit for it:)
 
Hmm. A few things come to mind worth checking:

- Are you clamping the body into the drill jig before drilling?
- Have you made certain that the drill bit you are using is a snug fit in the jig without any wiggle?
 
5Kids - Sorry your are correct, it was Lighting Boy's video. Your site has been very helpful too!

VK - I have not been clamping the body because it is such a tight fit, I had to work to get it both in and out of the jig. The drill bit came from DD4H, and is a snug fit.

I will take a little of the width off on the next go round and see if that helps. I was worried about drilling the axle holes after hollowing the body due to the potential for flex, but since that is what many of the more experienced racers do that's what I went with, as they know much better than I do! Hopefully reducing the width and loosening the fit a little will correct my issues.
 
I got a precision and a couple of jobbers from DD4H. I have been using the precision but I will check the jobbers fit to see if that is the case.
 
My first thought was that you need to sand your body so it fits better into the SB Pro... I think you may be flexing the thin hollowed body because it is so tight in the SB Pro. You body doesn't have to be tight at all in the SB Pro, it just has to stay in one place.... if it is a little loose clamp it.

The video you referenced is Lightning Boy's or Bulldog's... i think... not mine, but i would like to take credit for it:)
I ran into the same problem fitting into SB Pro and the Block several times this year, but only with the BSA kit blocks. I sanded the width down on a BSA block before cutting a 5/16" body, verified it fit into the SB Pro & The Block and routing it. When I finish routing the body, it still fit in SB Pro. No problems with DD4H sugar pine blanks.
 
I think I am going to glue and plug the rear axle holes with toothpicks, then sand down the width, check to make sure I have the right bit and fit, and redrill the axle holes to see where I end up. I'll try to report the results in a couple days.

Wags - the blocks were all BSA kit blocks. I have already cut one down into 3/8" planks, but for the next block I cut I'll sand the entire block to fit before cutting it into planks. On a side note it is crazy the amount of weight difference from block to block. Out of 6 blocks I have (2) less than 89 grams and the other (4) are all over 130 grams.
 
Thanks guys, I typed the wrong drill bit size used. I was using a #43 precision bit. I only ordered the precision in a #43 so I couldn't mistakenly grab the wrong bit for the SB Pro. I did order #43 and #44 jobbers to use in place of pin gauges to check tires with my home made run out gauge, but now have pin gauges to use.

Didn't get a chance to look at anything last night. This morning I filled the rear holes with toothpicks and wood glue. Hopefully tonight I will get a chance to put the calipers on the bit I was using, sand down the body to fit the SB Pro better, and re-drill.
 
Update - Verified both of the #43 bits at .0875. There is a tiny bit of slop between the bit and SB Pro bushing. Sanded block down and temporarily installed (12) cubes in the rear. Once I had a snug but not crushing fit I clamped and re-drilled. Both rears migrated like they should this time, however, one of the axle holes is still slightly off front to back. Using a pin gauge in the axle hole and a carpenters square on the block side to check there was just a slight amount of day light between the pin and the square toward the end of the pin. I suppose it could be the body is slightly out of square after sanding, going corner to corner their is about 1/32 difference, but that could be because the nose is tapered which could cause a inconsistent nose tape placement. I'll put it on a combo square next.
 
You might be better off to set the body in the SBP with the axle holes outside, but near, to the end of the jig so you could eyeball any toe in the pin gages against the machined end of the jig?
 
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I will give that a try, seems much easier than trying to hold a framing square on the side of the body.
 
You might be better off to set the body in the SBP with the axle holes outside, but near, to the end of the jig so you could eyeball any toe in the pin gages against the machined end of the jig?

I have done this along with using 1-2-3 block on the SB Pro jig and along the body. I feel that the size of the 1-2-3 blocks lets you move farther away from the point at which the axle enters the body and will help to identify smaller errors in the drill job easier.

If you don't have 1-2-3 blocks, a small machinist square also works quite well and is normally quite accurate as long as it is in good condition.

I have found multiple uses for the 1-2-3 blocks and small machinist square since I purchased them. If I were to start over, I would purchase them earlier in my learning curve.
 
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The 1,2,3 blocks are next on my need to purchase list, I'll add a small machinist square to the list as well.
 
I have found multiple uses for the 1-2-3 blocks and small machinist square since I purchased them. If I were to start over, I would purchase them earlier in my learning curve.

That is a true statement there! If I had known to check my drills to the extent that LB showed I now I would have gotten faster, faster. lol
 
That is a true statement there! If I had known to check my drills to the extent that LB showed I now I would have gotten faster, faster. lol

Is that like ....quicker, faster or is it faster, quicker? :) Sorry, I couldn't resist.

And yes the 1-2-3 blocks and machinists square have been a great addition to the tools!