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AlanMJackson
09-01-2014, 04:21 PM
Hi,

I've got a homemade CNC machine, 3 axis, mostly made of MDF. I'm new to CNC machines.

I want to drill lots and lots of 10mm holes in wood. The holes will go right through the wood and are 45mm deep.

What kind of tool would you use for that?

Right now I've fixed a bosch hand-drill in the machine and I'm drilling the holes with a 10mm brad point drill bit. To get a good finish on the surfaces I'm drill from both sides and meeting in the middle. If I try drilling all the way through it just blows out badly on the bottom surface.

I'm not getting that great a finish anyway (the drill is pulling fibres up) and it is taking an age! The maximum feed speed I'm using is 50mm/min and my program to drill 120 holes is taking over 90 minutes.

I imagine I want to fit the router head and put some kind of end mill in there but I don't know what.

Any help very gratefully received!

Lee Roberts
09-01-2014, 07:46 PM
Hi Alan welcome to the forum!

Is the blowout on the bottom because your not using a spoil board under the stock? It sounds like it. If you do the above that should stop the blowout and allow you to get the depth you want so in this case a through cut/hole.

Is the feed speed of 50mm/min the plunge speed or the speed your moving to the next hole? It sounds like the hand drill is spinning the bit to fast.

Fitting the router would be the better option I would think, you could then (hopfully) setup the correct rpm for that size bit, if your doing drilling like that then a nice sharp slot drill would serve you well, however what you should probably be doing is something called peck drilling, this is where you drill down into the hole 1 or 2mm a time, rasing back out of the hole after each plunge/cut, this helps to clear the chips, keep the cutter cool and do the drilling in a nice controlled way.

You could go with a smaller end mill say something like half, so a 5-6mm diameter, you would then machine out the holes to the 10mm size you need. A standard end mill would work but a drill bit would be better as end mills are designed for cutting sideways rather than drilling.

.Me

AlanMJackson
09-01-2014, 09:30 PM
Thanks for the welcome!

I have tried with a spoiler board of plywood but that didn't help. Or rather it did help a bit but didn't stop the problem.

I'm using a Colt 10mm brad point drill bit - a normal HSS wood drill bit for a hand drill. The wood is pine.

You think the hand drill is spinning too fast? I can slow it down. The top speed of the drill is probably something like 2000rpm.

The 50mm/min is the plunge speed. The traverses between holes are much faster.

Would peck drilling, with all the up and down movements, ultimately be faster?

When you say "drill bit" do you mean the kind of bit you'd put in a hand drill / drill press or do you mean some kind of special end mill for drilling you'd use in a router head? I'm presuming you can't put a normal drill bit in a router head because it would spin too fast. The router head I have is a cheap hand router with limited speed control. Can you recommend a router head?

Thanks!

JAZZCNC
10-01-2014, 12:40 AM
You want a router dowel drill like this Wealden Tool Company Limited Dowel (http://www.wealdentool.com/acatalog/Online_Catalogue_Dowel_51.html)

Unfortunatly the size you want is showing out of stock here but will give you idea of what to look for.

You may need to peck but just do 2 -3 pecks to clear the hole.

mekanik
10-01-2014, 11:46 AM
Dowel drill 10mm diameter x 35mm (http://www.acefixings.com/index.php?option=shop&page=shop.product_details&product_id=3696&l=uk&utm_source=google&utm_medium=base&gclid=CMHLrt3C87sCFc7JtAod-DoAWQ)
This is a bit pricey if you are in a rush to get the job done, i am fortunate and have a lathe so make a split collet to fit my router and adjust the speed to suite, i use a standard drill, grind it flat bottom then just relieve the centre so you are cutting on two points(works a treat)
Regards
Mike

mekanik
10-01-2014, 12:07 PM
oops! sorry about that the one shown isn't long enough, ground drill will be fine
Mike

mekanik
10-01-2014, 12:22 PM
Gave Wealden a ring and they are expecting restock 28th Feb

AlanMJackson
11-01-2014, 12:26 AM
Hi Mike,

Thanks for calling Wealden!

I assumed the flutes on a normal drill are too steep to run fast in a router but you're saying it will work if I flatten the bottom and recess the middle? What speed would I run the bit at? And can you recommend a reasonably cheap router head?

Many thanks!

AlanMJackson
11-01-2014, 12:29 AM
Thanks for the advice JAZZCNC!

When you don't know the word for something it's really hard to search for it. It looks like "dowel drill" are the magic words!

mekanik
11-01-2014, 11:32 AM
Hi Alan
Can you give us some idea of what you are trying to make/what size/what quantity and the accuracy required on your hole location ? even if you could fit a router to your machine it wouldn't last very long working 9 hours a day so perhaps there's another option.
regards
Mike

AlanMJackson
11-01-2014, 11:08 PM
Hi Mike,

I'm making some reconfigurable shelving. I'm drilling a line of holes along lengths of wood, about 40 holes per metre. As mentioned before the holes are 10mm through holes and 45mm deep. Because I'm drilling from both sides to get a good finish I'm actually drilling 80 holes per metre but if I could get a good finish on both sides drilling straight through I could save lots of time.

If I could get accuracy of 0.5mm for each hole that would be great. Even 1mm would probably be fine. So I don't need much accuracy.

With help and ideas from the forum I've tried some experiments today and found I can get feed rates of 400mm/sec but the surface finish is poor. So I've written some drilling gcode that feeds at 50mm/sec to break the surface for a few mm then goes to 400mm/sec for the rest of the drill cycle. Which means I've halved the program time and I'm now doing a metre in half an hour.

I've got a batch of 25m to do now and I'll be wanting to do 100 - 200m soon. I ran the hand drill for about 6 hours the other day and about 2 hours today. So it looks like I'll be running the machine for a few hours a day.

Lee Roberts
11-01-2014, 11:35 PM
With help and ideas from the forum I've tried some experiments today and found I can get feed rates of 400mm/sec but the surface finish is poor. So I've written some drilling gcode that feeds at 50mm/sec to break the surface for a few mm then goes to 400mm/sec for the rest of the drill cycle. Which means I've halved the program time and I'm now doing a metre in half an hour.

Hi Alan,

That is good news i'm glad your getting somewhere with it, I'm now wondering if you could go all the way through with the holes but on the last few mm drop back down to 50mm/sec and hope for the same finish as the top?

.Me

AlanMJackson
11-01-2014, 11:55 PM
Hi Lee,

It's a bit of a basic question, but how do you get a good finish on the bottom surface when through drilling wood? Even when I do this by hand on a drill press I find this hard. I use sacraficial wood underneath but the holes still blow out. Do you need to clamp down really hard?

I like your idea of slowing down again for the bottom surface but even when I feed slow the whole way it was blowing out so I must be doing something wrong.

-Alan

Lee Roberts
12-01-2014, 12:57 AM
Hi Lee,

It's a bit of a basic question, but how do you get a good finish on the bottom surface when through drilling wood? Even when I do this by hand on a drill press I find this hard. I use sacraficial wood underneath but the holes still blow out. Do you need to clamp down really hard?

I like your idea of slowing down again for the bottom surface but even when I feed slow the whole way it was blowing out so I must be doing something wrong.

-Alan

No I think your right Alan, it is generally difficult to drill wood without getting any blow out on the other side of the hole, what I was suggesting was that by lowering the feed rate on the final pass’s may produce a better result than what your currently getting.

You see if you was to use an end mill and also combine something called ramping, I would think you would be eliminating some of the downward force produced (as we know) from trying to drill a hole with a normal drill bit (as the drill pass’s out of the wood the tip push’s the material away before its had a chance to cut it), though I must say I find using a sacrificial piece of wood under the hole I’m drilling sufficient allot of the time.

Using an end mill in this way would mean more force sideways and mean you’re using the side of the cutter, rather than the bottom.

I really don’t like the idea that you are using a hand drill on the machine, though I guess for this job using a hand drill for the spindle, it’s probably the better option to use a drill bit.

.Me

AlanMJackson
12-01-2014, 03:24 AM
Hi Lee,

I agree about the hand drill - it's a real bodge. I'm using it at the moment because I haven't been able yet to work out what would be better. I've found trying to select the right end mill, especially for through hole drilling, is a bit baffling to the new comer! Also I don't have a spindle yet. Have you got any recommendations?

-Alan

AlanMJackson
12-01-2014, 03:35 AM
Do you think I should be using something like this?:

CNC Router Tooling Thru-Hole Drills. CT 70 mm length -Thru-Hole, Right Hand (http://www.cutter-shop.com/thru-hole-70-ct-rh.html)

AlanMJackson
12-01-2014, 04:23 AM
The plot thickens...

I'm going to use furniture bolts so I was planning to counter bore the holes. I imagined I would have to do that in another pass but it might be possible to do it in a single pass with a bit like this:

Wealden Tool Company Limited Drill Counterbore (http://www.wealdentool.com/acatalog/Online_Catalogue_Drill_Counterbore_53.html)

If I can find one big enough (10mm pilot, 16mm counter bore, 25+mm cutting length)... is that likely? I would have to counter bore on each face anyway so that would remove the advantage of through drilling if I could drill and counter bore at the same time.

GEOFFREY
12-01-2014, 08:13 AM
Hi, if you counter bore on both sides why is the finish on the under side a problem ? surely the c/bore will take care of this. If you get a spindle I think it would be much easier and you can use an end mill and program any hole size and counter you wish. Of course you will still have to turn the material over for the second c/bore. The break out on the underside could be eliminated if you use a down spiral cutter. Good luck with whatever you try. G.

JAZZCNC
12-01-2014, 10:43 AM
Thru drill like you posted will work resonably ok but depending on material and grain structure you will still possibly get some breakout.

Milling Holes is too slow and isn't often done for holes this size and in wood. Much quicker to drill just past half way with No or few Peck's then flip material and use same G-code.
This is really the only way you can guarantee no tear and If you find the Drill/Counter bore you need then this will save loads of time.

Also there's nothing wrong with using a Hand drill for drilling, that's what it's designed to do, just don't try using it for Milling that's when you have trouble.!

mekanik
12-01-2014, 01:06 PM
Hi Alan
A different perspective ?
I am not fortunate enough to have a CNC machine so do most of my stuff using jigs, with your equipment you could make a very accurate jig from MDF with it bored @ your required locations to suite a router guide bush,variable speed router would allow you to dial in the required speed and i can see no reason why 2 or 3 plunges should not complete a drilling(plus you can feel how it's cutting. would go with the bit that Dean suggested earlier as i think you need it scribing on breakthrough to try and negate breakout.
regards
Mike

AlanMJackson
13-01-2014, 01:31 AM
Much quicker to drill just past half way with No or few Peck's then flip material and use same G-code.


That's basically what I'm doing now. Thanks for the reassurance.

I haven't found the drill / counter bore combination I'm looking for yet. I'm looking for 10mm drill with 16 or 18mm counter bore. The largest I can find so far is 6mm drill with counter bore from trend. All the larger ones I've seen have a smooth short pilot just to locate the counter bore in the hole but not to drill it.

AlanMJackson
13-01-2014, 01:46 AM
Mike,

Do you think it would be possible to bore out the counter bore collar of something like this:

Trend CB58-14HSS 1/4 drill dia. x 5/8 counterbore (http://www.powertoolworld.co.uk/trend-cb58-14hss-14-drill-diameter-x-58-counterbore-hss-counterbore-sets.html)

so it would take a 10mm drill? Is that madness?

AlanMJackson
13-01-2014, 02:47 AM
Here's a picture of my machine in case you're curious what it looks like...

11270

irving2008
13-01-2014, 06:32 AM
Mike,

Do you think it would be possible to bore out the counter bore collar of something like this:

Trend CB58-14HSS 1/4 drill dia. x 5/8 counterbore (http://www.powertoolworld.co.uk/trend-cb58-14hss-14-drill-diameter-x-58-counterbore-hss-counterbore-sets.html)

so it would take a 10mm drill? Is that madness?

It might be possible but
a) there'd be 2mm less thread for the locking grub screw which may be an issue; and
b) you'd probably need to bore/drill it out in a lathe for any degree of accuracy in run-out.

GEOFFREY
13-01-2014, 07:53 PM
I would think that the counter bore is likely to be hardened steel so may be difficult to machine. If the thread depth on the grub screw is insufficient to get a good grip on the drill, you could try using say 3 grub screws. I would think it would be easier to use a fairly low quality drill (soft) and turn the shank down. G.