Drill press inaccurate - Woodworking Talk - Woodworkers Forum
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post #1 of 31 Old 10-07-2019, 05:19 PM Thread Starter
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Drill press inaccurate

I inherited an old drill press that my father bought used almost 50 years ago. It's done ok for me, but I've decided to buy a new 10" Wen drill press which is on its way. In the meanwhile, I'm still trying to get by with the old one.

I'm trying to drill 1/4" holes through 2x3's, and I find that when the drill comes down, the point of the bit often shifts from where it came down, so the hole can be upwards of 1/16" off from where I wanted it. The surface of a 2x3 isn't perfectly flat like milled dimensional lumber. So when the drill bit comes down, it seems to roll of the side of a hill before starting its dig.

Is there anything I can do to ensure a more accurately located hole? Drill a smaller pilot hole first?
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post #2 of 31 Old 10-07-2019, 05:25 PM
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is the wood securely clamped to the DP table or just hand held ?
a pilot hole will always make things easier.
hard and soft grain patterns also make things difficult.

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post #3 of 31 Old 10-07-2019, 05:49 PM Thread Starter
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I have an alignment jig clamped to the drill press table and I handhold the work piece against it.


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post #4 of 31 Old 10-07-2019, 05:50 PM Thread Starter
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I don't know why the image isn't showing up in my post. It shows up when editing.


http://pat.ssih.com/images/drillpress.jpg

Last edited by enchant; 10-07-2019 at 05:53 PM.
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post #5 of 31 Old 10-07-2019, 06:11 PM
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A "center drill" like the tool makers and machinists use, will make a significant improvement in your drilling accuracy. They come in many sizes and are easily found at places like Grainger, Johnstone Supply, WTTool, etc. Look at the bit he's using in this video. It's short and stubby for a reason. Although he's using it to drill metal these bits will work very well in wood too. I have many sizes. Some come with the bit shape on both ends and some only have it on one end. We woodworkers can learn a lot from machinists and tool makers when we want to be more accurate. Just make an accurate "starter hole" with one of these, and it will improve your drilling accuracy significantly. It's also always a good idea not to attempt drilling a large hole in one step. Use a center drill, then step up to larger and larger drill bits until you reach the desired size.


Amazon offers a set of them.

https://www.amazon.com/Center-Drill-...0482644&sr=1-3


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Last edited by CharleyL; 10-07-2019 at 06:16 PM.
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post #6 of 31 Old 10-07-2019, 06:23 PM Thread Starter
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I was completely unaware of center drills. My order has been placed. Thanks!
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post #7 of 31 Old 10-07-2019, 06:59 PM
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If you have been using the standard twist drills, it is probably that the bit has been drifting because of the grain in the wood. Nothing to do with the drill press. Smaller diameter bits will drift more than larger diameter.



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post #8 of 31 Old 10-07-2019, 07:00 PM
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The quill may be a sloppy fit on your drill press, either from wear or just the way it was made. Look @ the front of the drill head. Is there a slit that runs vertically down most of its length? If so, there are adjustment screws used to tighten the clearances to the quill. One or 2 screws will be there to pull the clearance tighter and one will be there to press the clearance open. When you get the proper setting the screws should all be snug so the gap can't change. Drilling with small diameter bits can be a problem because they flex too much. The most common length of bit is called "Jobber." In small diameters they can flex quite a lot. The usual option is to use "screw machine" bits, some times called stubys. They are quite a bit shorter but of course limited in the depth they can drill. Center drills come in several point angles and tapers of the main part. The most common point is 120 degrees which closely matches the jobber 118. The taper will be either 60 degree matching the live center on a lathe or 88 matching the taper on the typical counter sunk screw head.
You can also get bits that have a small center point that helps locate the start and outer spurs to cleanly cut the sides of the holes.
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post #9 of 31 Old 10-07-2019, 07:47 PM
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Quote:
Originally Posted by enchant View Post
I was completely unaware of center drills. My order has been placed. Thanks!
Err, a slight error in terminology was made in the initial post describing those drills. Center drills are not for drilling the center of a hole for a larger bit. Center drills are designed to drill a 60 degree cone in the end of a workpiece to allow for the use of a lathe center for turning operations.

What you use to locate a hole is a spotting drill. A spotting drill will generally have a wider angle on the tip than a standard twist drill, usually a 120 degree angle for a 118 drill. This is important because it allows the tip of the drill locate itself in the center of the cone drilled with the spotting drill without the edges of the drill hitting the workpiece. The tip of the drill is what guides it, you want it to be what makes first contact. If you try to use a center drill, which will leave a 60 degree cone, the edges of the drill will cut before the point, which will lead to your bit wandering.

All of this is completely irrelevant anyways, because what you need is actually a center punch. A spotting drill is best used on a ridgid machine to place an accurate starting spot for a longer, less stiff drill. On something like a milling machine, the quill is going to be rock solid and any inaccuracy in the hole location is more likely to come from the drill itself flexing, starting with a short, stiff spotting drill will put the initial spot on target, after which the longer, more flexible drill will center itself on the spot and drill where you want it to. On a less rigid machine, like your drill press, the quill is more prone to moving, so any sort of spotting drill on it wont help. A center punch will put a dimple where you want the hole to go, and then the drill tip will center itself in that divot and put the hole where you want it.

It might all sound pedantic to some, but theres something to be said for using the proper tool for the job. A quick tap with a center punch and a sharp drill where put a hole exactly where you want it 99.99% of the time, even with an inaccurate machine, but trying to accurately locate a hole with an inaccurate machine will be an exercise in frustration, even with the proper drills
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post #10 of 31 Old 10-07-2019, 10:03 PM Thread Starter
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Quote:
Originally Posted by epicfail48 View Post
Err, a slight error in terminology was made in the initial post describing those drills. Center drills are not for drilling the center of a hole for a larger bit. Center drills are designed to drill a 60 degree cone in the end of a workpiece to allow for the use of a lathe center for turning operations.
Be that as it may, it sounds like it might improve my situation a lot. One of those center drills has a 1/4" larger size, which is what I'm looking for. If I get a slight depth at that diameter located properly, the regular drill bit should drill the rest of the way just fine.


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All of this is completely irrelevant anyways, because what you need is actually a center punch.
That isn't really what I'm looking for. I need to drill holes in a lot of pieces of wood. I've created a positioning jig and I'd like to just take piece after piece, put it in the jig and drill the hole. I don't want to have to measure and mark every piece.
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post #11 of 31 Old 10-08-2019, 12:35 AM
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Hi


It looks like you have the same type of DP I have, a Delta Homecraft and you more then likely have some play in the quill bushings. So no matter what you do you will have a little bit of drift until you can get someone to make new bushings.

Last edited by ajdragon; 10-08-2019 at 12:53 AM.
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post #12 of 31 Old 10-08-2019, 01:39 AM
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In my great and unmatched wisdom I see you were given two valuable pieces of advice, post 8 and 9 pretty well sum up drilling accurately.

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post #13 of 31 Old 10-08-2019, 05:34 AM
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I'd like to see your locating fixture ......

Quote:
Originally Posted by enchant View Post
Be that as it may, it sounds like it might improve my situation a lot. One of those center drills has a 1/4" larger size, which is what I'm looking for. If I get a slight depth at that diameter located properly, the regular drill bit should drill the rest of the way just fine.



That isn't really what I'm looking for. I need to drill holes in a lot of pieces of wood. I've created a positioning jig and I'd like to just take piece after piece, put it in the jig and drill the hole. I don't want to have to measure and mark every piece.

OK, so no measuring and marking and swapping out short drills to longer ones.
A spur bit or brad point drill, is the first thing that came to my mind like this:
https://www.woodcraft.com/products/f...xoCxFAQAvD_BwE

https://www.amazon.com/Bosch-B14603-.../dp/B0065EPHSK


Then you need to increase your RPMs so the bit will cut immediately and not wander around. RPMs should be between 1500 and 1000 but a higher speed may work better, I donno? Experiment with speeds until it works. This bit has a sharp point on the end that will dig in and locate the hole properly. It won't wander like a ordinary twist drill, typically used in metal. This bit is made for wood only.
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Last edited by woodnthings; 10-08-2019 at 05:47 AM.
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post #14 of 31 Old 10-08-2019, 06:28 AM Thread Starter
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Thanks, everyone, for all the help and advice. I appreciate the education. And I want to mention that I did NOT buy this new Wen drill to solve this particular problem. That was for other reasons. But I have to suspect that this problem could happen with any DP, so it's best I come up with a solution.


The center drill bits are on their way, so that will be my first attempt at a solution. If they don't work, I'll try some of the other suggestions.
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post #15 of 31 Old 10-08-2019, 12:50 PM
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Drill bit speed chart that may help:

http://sawdustmaking.com/Free%20Charts/Bit%20Speed.pdf

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post #16 of 31 Old 10-08-2019, 12:58 PM Thread Starter
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Printing that.
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post #17 of 31 Old 10-08-2019, 02:15 PM
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Other charts here if interested:

http://sawdustmaking.com/Free%20Charts/charts.html

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post #18 of 31 Old 10-08-2019, 08:23 PM
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Quote:
Originally Posted by ajdragon View Post
Hi


It looks like you have the same type of DP I have, a Delta Homecraft and you more then likely have some play in the quill bushings. So no matter what you do you will have a little bit of drift until you can get someone to make new bushings.
This sums up most of my following response pretty well. If you have play in the quill, it doesnt matter what type of drill bit you use, its going to wander.

If you want every piece you make to match, you either need a jig that guides the drill bit itself, not just locates the work, or you need to take the extra time to center punch your holes. A spotting drill will still give you a spot at the wrong location, because as already mentioned the drill bit isnt what wanders on an old too, its the entire quill. A center drill will do the same thing, with the added benefit of being the wrong tool for the job.

Final thing, play in the quill isnt something that happens with any drill press. Play in the quill happens with a poor quality or misadjusted press. My 1930's Delta floor drill has no real play after i restored it. Before that, i learned to work around the play, and have no trouble saying i can drop a hole inside a few thou of where its supposed to be

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post #19 of 31 Old 10-08-2019, 09:39 PM
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A good way to accurately drill holes is to use a fixture with drill bushings. The come in HSS or carbide, with or w/o flanges. Places that sell to metal machinists have them. McMaster-Carr, Fastenal, Carr Lane, MSC, ... Machinists put them in metal plates but I suspect you could use maple as the fixture. If your project has a lot of pieces it might be worth it to have a machine shop make your fixture in metal. They should be able to give you 0.001" accuracy. When drill bushings become worn they are just pressed out and a new set pressed in. The fixture remains the same.
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post #20 of 31 Old 10-09-2019, 06:06 AM Thread Starter
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Originally Posted by epicfail48 View Post
If you want every piece you make to match, you either need a jig that guides the drill bit itself, not just locates the work, or you need to take the extra time to center punch your holes.
So how about this... What if, rather than drilling a preliminary pilot/centering hole, I mount the center punch in the drill press, and with it turned off and using my alignment jig, put the the center punch dents into my wood that way?
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