drilling with precision

[Dan Gaylin]

Sorry for the dumb question, but one of my biggest challenges with my projects is drilling precisely placed holes. I have a drill press (not the best the Wen variable speed benchtop unit), excellent drill bits (Lee Valley Brad points and Norse twist split points). I measure and mark carefully. I use a center punch to create a dimple. And yet, I still have a lot of problems.

Here's a typical example of the problems I have: I was recently attaching a wooden platform to a linear rail guide. The sliders that move on the rail guide have four metal threaded holes for machine screws. So the platform sits on top of the sliders and is attached to the sliders with the machine screws. In order for this to work, I have to be able to drill the holes through the platform so that they almost exactly match the locations of the holes on the sliders. So I took a thick piece of card stock and made a template by punching through the card stock into the holes. I then used the template to mark the hole locations on the platform, and used the center punch to make dimples on the wood. I then used the drill press to make clean straight holes at each location. And yet.... when I went to attach the platform to the sliders (4 in total), some of the holes were off a little bit, and the screws did not go straight into them. So the results was that the platform was not square on the rails and thus didn't slide smoothly. So I did what I often have to do which is use a bigger bit than I want to and enlarge the holes, so that things "fit". But of course now the platform was moving around a bit, so while it slides smoothly, it doesn’t track properly.

I don't understand how I consistently get things like this just a little bit off, but it is quite frustrating. For sure the drill press has a little bit of wobble, but it is pretty small. And this happens to me when I do even simpler things (and also when I making things without the drill press and doing it by hand, with a very good Bosch hand drill and careful measurement) Any thoughts or suggestions would be appreciated.

Thanks,

-dan

[Tom Dixon]

Sorry for the dumb question, but one of my biggest challenges with my projects is drilling precisely placed holes. I have a drill press (not the best the Wen variable speed benchtop unit), excellent drill bits (Lee Valley Brad points and Norse twist split points). I measure and mark carefully. I use a center punch to create a dimple. And yet, I still have a lot of problems.

Here's a typical example of the problems I have: I was recently attaching a wooden platform to a linear rail guide. The sliders that move on the rail guide have four metal threaded holes for machine screws. So the platform sits on top of the sliders and is attached to the sliders with the machine screws. In order for this to work, I have to be able to drill the holes through the platform so that they almost exactly match the locations of the holes on the sliders. So I took a thick piece of card stock and made a template by punching through the card stock into the holes. I then used the template to mark the hole locations on the platform, and used the center punch to make dimples on the wood. I then used the drill press to make clean straight holes at each location. And yet.... when I went to attach the platform to the sliders (4 in total), some of the holes were off a little bit, and the screws did not go straight into them. So the results was that the platform was not square on the rails and thus didn't slide smoothly. So I did what I often have to do which is use a bigger bit than I want to and enlarge the holes, so that things "fit". But of course now the platform was moving around a bit, so while it slides smoothly, it does track properly.

I don't understand how I consistently get things like this just a little bit off, but it is quite frustrating. For sure the drill press has a little bit of wobble, but it is pretty small. And this happens to me when I do even simpler things (and also when I making things without the drill press and doing it by hand, with a very good Bosch hand drill and careful measurement) Any thoughts or suggestions would be appreciated.

Thanks,

-dan

So my take on your particular problem in this one instance is that you relied on marking a cardboard template by punching holes and expected to be able to accurately transfer that to the wood you planned to drill. The only way to achieve accuracy is to measure the exact distances on the slider and then measure those same exact distances on the piece you intended to drill, punch them and verify the measurements are still correct after punching them. One thing that sometimes will help though for alignment is to drill the hole 1/32 or .5mm larger so there is some play for the screw passing through that hole into the threads on the slider but not so much larger so as to allow the piece to be out of square. like when you enlarged your holes. There is no substitute for accurate measurements.

[Tom M King]

Transfer punch, or VIX bit through the holes in the bearing mount directly onto the piece of wood. Measuring, and transferring will always introduce some error.

[Tom Dixon]

Transfer punch, or VIX bit through the holes in the bearing mount directly onto the piece of wood. Measuring, and transferring will always introduce some error.

The OP will need to verify but I don't believe these are through holes so pretty much impossible to transfer punch or use a VIX bit if they aren't. It would be helpful if the OP could post a photo of the slider he is trying to drill wood to mate up to.

[Andrew Seemann]

You didn't mention your material, but some woods, like Doug Fir, can have very hard growth rings relative to the softer parts of the wood, and can actually deflect your bit. Softwoods tend to be more prone to this, as some varieties have much harder late wood than early wood, but it can happen with hardwoods also.

[Brian Holcombe]

Your approach to transferring is one point of issue, but it’s mentioned above.

- Use the shortest bit possible.

- Check the runout at the Chuck.

- Chevk to see if the table is square to the spindle. (Sweep the table in a radius with an indicator)

- use line boring bits and not twist drill bits.

[Tom M King]

The OP will need to verify but I don't believe these are through holes so pretty much impossible to transfer punch or use a VIX bit if they aren't. It would be helpful if the OP could post a photo of the slider he is trying to drill wood to mate up to.

He wants to attach the wooden platform to the linear bearings with machine screws, but didn't say if the threaded holes went all the way through the bearing bases. The ones I've used do. Transfer punches are for sheet metal. They fit tightly inside threaded holes, but would probably still work better than measuring for wood. A VIX bit could also work if there was a properly sized one, and if there is access for one.

I have even used set screws to transfer before. I can never measure, and transfer perfectly every time either.

A picture would help a lot.

[Dan Gaylin]

Thanks for the replies. Yes the flaw with the sliders is that they are not through holes so I can’t put something through them to center the drilling. The wood is poplar. I don’t have a picture because this is a couple of months back now and I disassembled it in frustration. I agree that there is no substitute for accurate measuring and I like the suggestion of measuring, dimpling, and measuring again. I just thought the template approach would be more accurate and repeatable than measuring every time. Should I maybe have used a thin piece of polycarbonate to make the template — would allow me to see the hole and drill into it and then is a more solid template?

[Lee Schierer]

For transferring blind holes to a piece of wood, Get some cone point set screws and screw them into your threaded holes by hand so the points are sticking out. Then align your piece of wood on top of the sliders and set screws. Once you are satisfied with the alignment tap the wood on top of each set screw and you should have a divot where the hole needs to be.
socket-set-screw-cone.gif

One thing to remember, a 1/4 in screw normally won't go through a 1/4" hole you need to drill a slightly larger hole.

[Andy D Jones]

In machining metal, a center drill (fluteless, short, rigid drill bit) is often used to drill a shallow, conical pilot hole in a precise location. Then a spiral bit will center on the conical hole and maintain the precise location.

Something like that my help here.

Andy - Arlington TX

[Tom M King]

Set screws are handy things to have, sometimes for things you don't plan on. I have a small toolbox drawer full of them up to 1". I recently had to enlarge some threaded holes in a tractor block, and after that, had to enlarge the holes in the loader frame that would be bolted in place with the new, larger bolts. There were two existing holes that could be reused, so I only needed to enlarge a couple on each side of the tractor. The mounting brackets were bolted on with the good, original sized holes. I put set screws in the holes, with the Allen head facing out. I slowly enlarged the holes in the loader mounts with a 1/4" die grinder, until I could screw the set screws out through the hole, without taking off any more than I had to inside the holes.

I've used them for such transfer, as is needed here, too. Get the ones with the points already on them. Without metal machining equipment (lathe) you can't grind them to a point by hand, and have the point perfectly centered, like you need it.

[David Buchhauser]

Thanks for the replies. Yes the flaw with the sliders is that they are not through holes so I can’t put something through them to center the drilling. The wood is poplar. I don’t have a picture because this is a couple of months back now and I disassembled it in frustration. I agree that there is no substitute for accurate measuring and I like the suggestion of measuring, dimpling, and measuring again. I just thought the template approach would be more accurate and repeatable than measuring every time. Should I maybe have used a thin piece of polycarbonate to make the template — would allow me to see the hole and drill into it and then is a more solid template?

Hi Dan,
Most of the "sliders" (linear bearing blocks) manufacturers or sellers will provide some sort of documentation with dimensioned drawings showing the hole pattern and the distance between the centers of the holes. I would first lay out this pattern on a piece of 1/8" or thicker aluminum, polycarbonate, or something similar that you have available. With careful measurements and a sharp scribe and straightedge, you should be able to mark and center punch the 4 hole locations fairly accurately. Drill each hole first with a small (1/8" dia. or less) split point drill bit, then follow that with the correct size drill bit for the clearance hole for you attachment bolts/screws. (The split point will help to accurately locate the drill bit center onto you center punch marks.) You should be able to set this finished/drilled plate over the holes in the bearing block and visually make sure they are aligned, or even thread the bolts/screws into the bearing block mounting holes as a fit check. If all 4 holes align, then us your newly created "drill guide" by clamping it to the material you intend to drill your mounting holes into, and then drill them with your drill press (all 4 holes) before unclamping your "drill guide" from your material.

You can buy these bits as a set or individually at Home Depot. The smaller size individual bits cost around $3 to $5 each.


https://www.homedepot.com/p/Milwauke...4631/205879024

Milwaukee Split Point Drill Bits.jpg

Here is an example of the data sheet for some linear bearing blocks that I recently used for a project. I used the 15mm, so that would be the first line of the chart.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Linear Bearing Block Dimensions.jpg

I hope this helps.
David

[Dan Gaylin]

Thanks for all the helpful responses. I have a box of flat tipped “grub screws” but I was unfamiliar with the cone tipped ones. I will get some of those. The rail sliders did not come with a hole pattern with measurements, alas. Anyway I appreciate all of the advice.

[David M Peters]

Would you be able to drill the holes oversized? That would inform your choice of screws, pan head vs. flat head.