Drill or ream?

admin

I need to make some parts where I have to have a 18mm hole so I can tap it for 19mm threads.  However 18mm seems to be a really rare size drill bit.  Seems all I can find are China ones.  I tried a couple and they are supposed to be HSS, but a file bites right onto them like mild steel.  They won't drill at all.  I have different one ordered to try now.  Do you think I would be better of to drill the hole to a common size close to 18mm where I can get a quality bit easy, and then get a 18mm reamer and finish the holes with that?  Seems like reamers are easy to find.  Sent from my C811 4G using Tapatalk
Reply:11/32 drill bit will work for m19 tapI use this chart working on Japanese construction equipment with American drill bits https://littlemachineshop.com/Refere...DrillSizes.pdfLast edited by Firemanmike69; 02-15-2014 at 10:11 AM.
Reply:"11/32 drill bit will work for m19 tap"  Uh, no it will not.   18mm= 45/64" and that number is in its lowest common denominator.  But, 44/64" = 22/32" = 11/16".11/16" drill bit will give you a better, more precise fit with greater thread strength (slightly) than an 18mm hole.11/32" drill bit will likely result in much frustration when you try to engage the tap.
Reply:I looked on the wall chart from my local industrial supplier and it doesn't show 19mm. That size is approximately 3/4". the chart for 3/4-16 shows an 11/16" tap drill. ( I know, I know, 3/4-16 is not 19mm , I'm just sayin'). If we knew what metric thread your tap is, we could calculate the minor diameter and come close to guessing on a tap drill. 19 mm major diameter =.0748The chart suggests an 11/16 drill for 3/4-16. 11/16 = .687511/32 would be a little small since 11/32 = .34375Last edited by gnm109; 02-15-2014 at 10:46 AM.Miller Millermatic 252Miller Syncrowave 200Liincoln AC-DC 225Victor O-A Set
Reply:Originally Posted by gnm10919 mm major diameter =.0748
Reply:Ahh, yes. 19mm  x 2.50 tap requires 11/16 drill. Miller Millermatic 252Miller Syncrowave 200Liincoln AC-DC 225Victor O-A Set
Reply:If you can't find an 18mm drill bit it is because there is an acceptably close standard size available though McMaster does have one in a half inch shank and Morse Taper.Last edited by 76GMC1500; 02-15-2014 at 01:06 PM.
Reply:Thanks for the responses!  The thread is 19mm x1.0 pitch, which is extremely uncommon.  I did find a tap after much searching.  Most charts skip right over 19mm, and the ones that do have it only show 2.5 pitch.  I'll try the 11/16".Sent from my C811 4G using Tapatalk
Reply:Originally Posted by Firemanmike6911/32 drill bit will work for m19 tapI use this chart working on Japanese construction equipment with American drill bits https://littlemachineshop.com/Refere...DrillSizes.pdf
Reply:If you are threading a 1.0 pitch instead of 2.5 you are going to need to run a much larger bit for your hole.  You need to find the minor diameter of the thread and use a bit of approximately that size.  If you go less you will get a 100% thread profile which may not run free, most threads are 70-75% profile as that achieves the full strength, runs free, and is much easier on tooling.17.92 appears to be the recommended tap drill size.Last edited by 76GMC1500; 02-15-2014 at 09:49 PM.
Reply:Originally Posted by JustmeThanks for the responses!  The thread is 19mm x1.0 pitch, which is extremely uncommon.  I did find a tap after much searching.  Most charts skip right over 19mm, and the ones that do have it only show 2.5 pitch.  I'll try the 11/16".Sent from my C811 4G using Tapatalk
Reply:Originally Posted by JustmeThe thread is 19mm x1.0 I'll try the 11/16".
Reply:Shoot!  Guess it's good I didn't try the bit I bought today.  I'll wait for the next 18mm one I ordered.  Hopefully is actually HSS!Sent from my C811 4G using Tapatalk
Reply:19mm X 1-0 !That is a "very fine" thread.  Good thing the discovery process went deep enough to reveal this.
Reply:not only a "very fine" thread, but (and my previous job was designing machinery, using all kinds of bolts) one that is very, very odd... So odd that I have trouble believing it even exists... must be a one of a kind thing.
Reply:Originally Posted by kingneronot only a "very fine" thread, but (and my previous job was designing machinery, using all kinds of bolts) one that is very, very odd... So odd that I have trouble believing it even exists... must be a one of a kind thing.
Reply:And with 17.92 mm being the recommended size, 45/64 puts you pretty much dead on.  That's .002" over or .06mm
Reply:Drill error is often up to .005 anyway, get close and go to townExperience is something you get right after you need it
Reply:Originally Posted by walkerweld19mm X 1-0 !That is a "very fine" thread.  Good thing the discovery process went deep enough to reveal this.
Reply:I hope you intend to use a drill press or other means of securely holding that tap because it is a bottoming tap for sure.But from your posts I think you have a good grip on the situation.
Reply:Originally Posted by walkerweldI hope you intend to use a drill press or other means of securely holding that tap because it is a bottoming tap for sure.But from your posts I think you have a good grip on the situation.