[Goonk]

I installed a waste spillboard on top of my spillboard and decide it would be nice to drill some 1/4" holes along X and Y to use as locaters (every inches). By inserting 1/4" dowels (really nice ones I found at Amazon +0.001 -0.000), I could then align my workpiece to X and Y. Well, when I put my dowels in the holes I drilled, they wobble a fair amount.

So, that got me to wondering what is the best way to drill accurate hole? My machine is a 2448 standard Mach3, Bosch 1617, VCarve. I checked the runout on my router and it was 0.001 or so (suprised me!). Can't remember how to define runnout exactly, but it indicator only moved 0.001. My bit is a brand new upcut Amana 1/4". It checks very close too. I think I used the peck method of drilling. I also noticed yesterday when doing a project that when cutting holes, the router raised all the way up to the safe Z height each peck. Seems like I saw a settingfor that (adds lots of time and useless motion).

Still learning!

Any tips on precision hole driling?

I know I need to sure up my base. It is moving around a fair amount.

Thanks,

Tony

[CitizenOfDreams]

If is not physically possible for a drill bit that measures exactly 1/4" to make a snug fit hole for a dowel that measures exactly 1/4". Since you have a working CNC router, you can use a smaller end mill (like 1/8") and interpolate a hole of any size you need. Start with an undersized hole and open it up if the dowel fits too tight.

[nlancaster]

Use your 1/4 inch end mill to peck drill the holes. worked great on my table, 1/4in dowels are a snug fit in the holes.

[bonesbr549]

Funny I was just playing with this this not to long ago. First, use a set of calipers to measure your pins to ensure they are infact .25. Next use a bit that is smaller than the hole and do pocket path to get to the exact width. I had 6mm pins and used a 1/8" bit and did a pocket path, and left a bit for a profile pass.

my pins were not exactly 6mm so I redid (test) with .001 under 6mm and they are snug. I cut a dozen and they worked well. I'm sure if If both were dead on it could be diff.

[Goonk]

Thanks for the help.

My dowels do meaure as advertised - barely a thou or two over 0.250. I was using a 1/4" bit and peck drilling. That didn't result in a 0.250 hole! I'll try using the smaller bit and see how that works. I'm going to play around with it some more and see what I can figure out. I can't imagine the machine moving during drilling. I have not checked my bit for runout. That's one part of the equation. Also haven't checked other bits. So, just getting started. I just wanted to check and see if there was a better drilling technique for accuracy. I checked the router using a dial indicator on the chuck and it barely moved, so that was encouraging.

Thanks!

Tony

[LeeWay]

Twist drills do not always drill round holes. This is why it is much better to interpolate the holes if you are looking for accuracy and a round hole. This is more apparent in thin materials with cheap bits, but does occur with good bits in thicker materials too.
The top of the hole can also be larger than the bottom of the drilled hole. For the best precision, a reamer is used after drilling, but for speed and the tolerances you are probably looking for, interpolation of a smaller tool is probably the best. In my mill, I always drill a smaller hole and then interpolate to the required size.

[Goonk]

Thanks. I am using "good" mills. I'll try my 1/8" bit this weekend and experiment with sizes until I get a good fit.

Tony

[hanermo]

Drills are not even remotely accurate, or straight, or on size rerecision.

But what is precision, for You ?

Fast A.
Bore the hole to finish, this makes it round and even.
Use a reamer to finish the hole.
This makes it about 0.01 mm on size, and it follows the bore.

A drilled hole is usually uneven ie not round, and it is generally banana-shaped.

For router use, maybe a suitable reamer, in 2 stages, if boring is not an option.
Ie drill 5.8, ream 5.9, ream 6.00.

In metals:
For better results, jig grind the holes, then roller burnish to finish.

For fast production like auto stuff, a diamond coated hone will finish a hole to a few microns, under 10 secs.
Better than 0.01 mm in size, very straight, very good finish.
It is really a rod with diamond stuff embedded in it.
Lasts a very long time, can be tens of thousands of workpieces or more.
Not very expensive.

A hobby guy can line bore + lap to about 1 micron, if they want to.

[Goonk]

I finally got around to testing some more holes. I used a 1/8" mill from ToolsToday. To start, I asked for 0.250 holes. It is hard to measure a hole that small accurately, but the dowels I have (Amazon - 1" machined dowels -0.000 +0.001 I think) fit very snug, so that was good enough. Thanks for the help.

Tony

[bonesbr549]

also u may want a few thou over. I did something similar to use my festool 20mm clamps. My test hole was so snug it was a pain to get them in our out. I did another test one thou over then two thou over. In the end the two thou was better. Good luck

[DaveCNCnewb]

Also considering making some "dogholes" in my table. I already put a shallow grid pattern on the spoil board. Lee Valley has some great new Veritas working holding clamps that should lend themselves to CNC work...


Veritas® Bench Blade - Lee Valley Tools

Sent from my SM-G930V using Tapatalk

[cncjack01]

[GigaWatt]

Also considering making some "dogholes" in my table. I already put a shallow grid pattern on the spoil board. Lee Valley has some great new Veritas working holding clamps that should lend themselves to CNC work...


Veritas® Bench Blade - Lee Valley Tools

Sent from my SM-G930V using Tapatalk

Those might be very useful, however considering the cost I would want some reviews for cnc work before purchasing them. Give us a review if you try them.

[DaveCNCnewb]

Ended up never buying those expensive clamps...thus no review. Lo and behold is what I think might be a better option for CNC that was just introduced by Kreg Tools. They're plastic which is good but I wonder if they have the holding power required.

https://www.kregtool.com/store/c29/b...in-line-clamp/

[GigaWatt]

Those look very interesting however I would also be concerned about strength. Hopefully someone will review them soon.

[DaveCNCnewb]

Those look very interesting however I would also be concerned about strength. Hopefully someone will review them soon.

I just ordered 4 of them and will let you know. I can always use them on my bench if they don't work for the CNC.