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View Full Version : CNC drill bit conundrum...



HankMcSpank
07-08-2009, 03:09 PM
I have a requirement to to drill 4.2mm holes to a specific depth in acrylic using my CNC spindle (I don't have a drill press & the depth of the holes have to be pretty accurate).

My problem is, 4.2mm drill bit shaft is too thick for a 4mm collet, yet too small for a 5mm collet (& I don't have a 4.2mm collet!) ...besides I'd rather not have to faff about changing collets where possible (that's a real time sump!). In the main I use a 3.2mm collet.

I'm having great success with these type of drills (which have a 3.2mm shaft)...

http://img33.imageshack.us/img33/9738/dremel.jpg (http://img33.imageshack.us/i/dremel.jpg/)

But they only do 3mm, 4mm, 5mm & 6mm :-(

I'm therefore considering, buying some cheap (soft) 4.2mm drill bits turning down the shaft using my lathe (once it works!) so the shafts fit in a 3.2mm collet ....is this plan flawed? (runout aside!).

Is there a better way? (ie somewhere I can buy 4.2mm bits with a 3.2mm shaft!)

HiltonSteve
07-08-2009, 04:13 PM
Buy a 4.2mm collet.......

Are you originally from Yorkshire by any chance?? :heehee:

HiltonSteve
07-08-2009, 04:28 PM
Have you tried pushing the drill into the 4mm collet with it off the machine?? You can sometimes 'stretch' collets for odd sizes, I found that if you take the collet out of the spindle and pushed the cutter through it from the back it would give enough to get it in.

Did not work every time though...

HankMcSpank
07-08-2009, 05:02 PM
It's a fair cop - I'm unfeasibly tight (I turn the grill off completely when I'm turning over beefburgers! lol ), but this isn't about avoiding buying a 4.2mm collet (for one, I don't think they don't make 'em for the spindle I have the loan of a Proxxon BFW 40/E), but it's more about having a quick/pleasant workflow - it's a pain in the ass to be constantly swapping collets!

Re pushing the 4.2mm into a 4mm collet...well I only have the loan of a collet set (from AudioAndy) & I wouldn't want to risk any 'issues' by coaxing/forcing!

Dean,

re my lathe - well I bought a knackered one http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=320402259056&ssPageName=STRK:MEWNX:IT (cos I refuse to pay retail...albeit second hand lathes almost meet retail prices on Ebay anyway!) ...it hasn't got a chuck (anyone got an 80mm they want to sell?) & as I established last night, the PCB is complete toast - just about every bit of silicon on that board is fried & I'm not paying 80 for a new one. John S put me onto a Danfoss board last night on Ebay & I've nabbed it for 15 - just got to work out how to adapt it to integrate into my Sieg!

oh yeah...then I'll have to start at page 1 "Lathes for Dummies". (which "Step up adapters" for all being ingenious is well outside the scope - fortunately, I've now found a source for some 4.2mm bits with a 1/8" shaft ....

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=250324771762&ssPageName=STRK:MEWAX:IT


Which wasn't easy to find as he hasn't listed any obvious keywords - just how does that happen...I've been searching for the best part of a fortnight - nowt, but as soon as I ask for help on here, my next Ebay search locates a source. Doh.

ptjw7uk
07-08-2009, 09:48 PM
Hank
Also on ebay
http://cgi.ebay.co.uk/CARBIDE-DRILLS-4-20MM-PACK-OF-5_W0QQitemZ250474015564QQcmdZViewItemQQptZUK_BOI_M etalworking_Milling_Welding_Metalworking_Supplies_ ET?hash=item3a516a2b4c&_trksid=p3286.c0.m14

Peter

HankMcSpank
07-08-2009, 10:01 PM
Hank
Also on ebay
http://cgi.ebay.co.uk/CARBIDE-DRILLS-4-20MM-PACK-OF-5_W0QQitemZ250474015564QQcmdZViewItemQQptZUK_BOI_M etalworking_Milling_Welding_Metalworking_Supplies_ ET?hash=item3a516a2b4c&_trksid=p3286.c0.m14

Peter

Thanks Peter...I can see why my search didn't locate that ad - I tried to find those ads with 4.2mm and 3.2mm in the ad body or 4.20mm and 3.20mm, (ie second decimal place) but look what he's done

Extract from his ad...


"4.20MM DIAM .WITH 3.2MM SHANK"

so I was caught by the seller's inconsistency! (also some sellers use the word 'shafts' others 'shanks' ...it all adds up mto a lot of permutations and possible 'misses')

Thanks once again

ptjw7uk
07-08-2009, 10:29 PM
Never have understood searching on Ebay as I have spent hours trying to find stuff I know I had seen on there a day or 2 earlier.

I do know that searching is the hardest think to program for as the slightest variation will give a no finf result bets to try wid cards if possible.

Peter

greenz123
06-07-2015, 11:02 AM
I have a requirement to to drill 4.2mm holes to a specific depth in acrylic using my CNC spindle (I don't have a drill press & the depth of the holes have to be pretty accurate).

My problem is, 4.2mm drill bit shaft is too thick for a 4mm collet, yet too small for a 5mm collet (& I don't have a 4.2mm collet!) ...besides I'd rather not have to faff about changing collets where possible (that's a real time sump!). In the main I use a 3.2mm collet.

I'm having great success with these type of drills (which have a 3.2mm shaft)...

http://img33.imageshack.us/img33/9738/dremel.jpg (http://img33.imageshack.us/i/dremel.jpg/)

But they only do 3mm, 4mm, 5mm & 6mm :-(

I'm therefore considering, buying some cheap (soft) 4.2mm drill bits turning down the shaft using my lathe (once it works!) so the shafts fit in a 3.2mm collet ....is this plan flawed? (runout aside!).

Is there a better way? (ie somewhere I can buy 4.2mm bits with a 3.2mm shaft!)


Hi Hank,

I have come across this exact same conundrum, the ebay link in the thread doesnt work anymore. I dont suppose you found anywhere that does drill bits with 3.175 shanks which have a larger diameter ?

HankMcSpank
06-07-2015, 11:57 AM
Hi Hank,

I have come across this exact same conundrum, the ebay link in the thread doesnt work anymore. I dont suppose you found anywhere that does drill bits with 3.175 shanks which have a larger diameter ?

Wow, that was an old post.....in the end I found a good Uk source for drill sizes larger than 3.175mm (but with a 3.175mm shaft), here you go...

http://www.acsind.co.uk/ ...I was dealing with - Dave Cornell (Technical Sales Engineer)...I don't want to post his email on an open forum (else bots will start spamming him), but if you want to email him direct, shoot me a PM)

...they do both new & re-pointed, being a tightwad, I bought re-pointed (but frankly I got great results with them & couldn't tell the difference vs. brand new), they have all manner of sizes available & the prices were excellent as were their postage charges (no affiliation!). I mainly bought sizes below 3.175mm as the cost does go up somewhat for sizes greater than 3.175mm...but I did order a spattering of larger sizes (e.g. 4.0mm 4.2mm 5.00mm 6.0mm & 6.35mm) all with 3.175mm shafts....a great time saver when you're only drilling acrylic.

Edit: I've just found the email with the prices I paid back in 2011 (just to give you an idea)...

10 off Repointed 1.60mm drills @ 4.49 in total (i.e. 44.9p each)
10 off Repointed 3.00mm drills @ 4.49 in total
10 off Repointed 3.175mm drills @ 4.49 in total

2 off Repointed 3.40mm drills @ 4.36 in total
2 off Repointed 3.60mm drills @ 5.14 in total
2 off Repointed 3.80mm drills @ 5.14 in total
2 off Repointed 4.00mm drills @ 5.14 in total
2 off Repointed 4.50mm drills @ 5.90 in total
2 off Repointed 4.80mm drills @ 6.68 in total
2 off Repointed 5.00mm drills @ 6.68 in total
2 off Repointed 5.50mm drills @ 7.56 in total
2 off Repointed 6.00mm drills @ 8.36 in total
2 off Repointed 6.35mm drills @ 9.00 in total

greenz123
06-07-2015, 03:01 PM
That's brilliant thanks, it will save a lot of time ! Much appreciated.

cropwell
06-07-2015, 05:37 PM
Can't you just cut 4.2mm pockets, or do you need to go to great depth ?