Anyone got a recommendation for a small company who can cost effectively drill and ream 6 off 20.0mm holes through AB2 bronze castings. 2 at 36mm deep, 4 at 14mm deep. I have the hand reamer - they need (say) 5 drill bits up to 25/32" to drill the holes in stages. Needs to be done this week - I drop in Wednesday pm, pick up Friday pm. Thanks a lot in advance for advice.
Thanks a lot Trek and Mike. Have tried both and others but no dice. Have bought 25/32" (9.84mm) reduced shank hss drill bit and will do it on brothers drill press starting say 4mm drill and stepping up drill bits in small stages. Not going to be a 5min job.............sorry I only got the 25/32 bit late this arvo - should have immediately posted that had a plan b
r13 maybe use a step drill. Bunnings sell them. Reduces the chance of a big drill bit ripping up the work piece.
Drilling brass or bronze with a drill bit can be nasty, although it's not usually all the drill bits fault but the lack of feed control and the rigidity of what's driving the drill bit.
Drill bits mostly have a positive rake on the cutting edge which is what you need for most materials your likely to drill but with brass and bronze that positive rake causes the cutting edges to want to feed into the work sometimes at a rate your unable to control.
To help stop this happening you can reduce the rake on the cutting edges to a negative rake by grinding flats on the cutting edges, perpidicular to the axis of the drill.
This can be done with nearly any type of grinder or an oil stone.
You can even just dull one cutting edge but that has a tendency to cause the drill to drill oversize.
The type of job your describing I would usually set up on the milling machine, drill to .5 mm undersize and finish to size with a single point boring bar.
If you do change the cutting edge rake remember to restore it back to a positive rake before drilling normal materials again.
Select to expand quoteTrek said..
r13 maybe use a step drill. Bunnings sell them. Reduces the chance of a big drill bit ripping up the work piece.
Thanks Trek yes have ordered a reduced shank 25/32" drill from AimsIndustrial hope it get here on time else I'm stuffed
Select to expand quoteJolene said..
Drilling brass or bronze with a drill bit can be nasty, although it's not usually all the drill bits fault but the lack of feed control and the rigidity of what's driving the drill bit.
Drill bits mostly have a positive rake on the cutting edge which is what you need for most materials your likely to drill but with brass and bronze that positive rake causes the cutting edges to want to feed into the work sometimes at a rate your unable to control.
To help stop this happening you can reduce the rake on the cutting edges to a negative rake by grinding flats on the cutting edges, perpidicular to the axis of the drill.
This can be done with nearly any type of grinder or an oil stone.
You can even just dull one cutting edge but that has a tendency to cause the drill to drill oversize.
The type of job your describing I would usually set up on the milling machine, drill to .5 mm undersize and finish to size with a single point boring bar.
If you do change the cutting edge rake remember to restore it back to a positive rake before drilling normal materials again.
Thanks a real heap Jolene I wasn't aware of that at all. We plan to use lowest speed on the drill press and Suttons Venom Endurance cutting fluid. We will try and achieve good feed control and clamp the castings down securely.
I see the method you describe here; is how the bloke is changing the rake what you are meaning and how you do it?
canadianhobbymetalworkers.com/threads/drilling-brass-bronze.820/
Will be starting on m8.5 holes of the pintle side arms and gudgeon to transom bolt holes. Is the rake change recommended for these smaller drills also? Great thanks again.
It's definately an advantage to adjust the rake on the smaller drill bits,, you can also reduce rake by reducing the relief angle aft of the cutting face but that requires grinding the cutting edges down until they are almost level with the trailing edge of the drill cutting face. That angle is commonly about 12 deg but reducing it to about 5 deg helps drastically. You can also put a small flat on that face of the cutting edges. It's easier to do it this way with small drills, bigger drills you are grinding alot of metal away.
Practice on an old drill bit and drill some holes in an old brass fitting of some sort.
All so be mindful that cutting fluid can sometimes lubricate too well and cause tool rubbing and work hardening if you're trying to go too easy especially on a 0 or negatively raked tool. Often a bit of pressure is required to start the cut and keep it going,, the cutting fluid can work against you trying to start the cut.
On a side note, I dislike the new Viper style drill bits with the multi facets. Although they centre nicely and drill beautiful, they lose alot of strength from behind the cutting edges and in a machine shop i have found it's not practical to have that style of point on a drill bit.
Many thanks again J. I will be Select to expand quoter13 said..Trek said..
r13 maybe use a step drill. Bunnings sell them. Reduces the chance of a big drill bit ripping up the work piece.
Thanks Trek yes have ordered a reduced shank 25/32" drill from AimsIndustrial hope it get here on time else I'm stuffed
Sorry - step drills different to reduced shank drill. Need the full depth to 36mm deep at 25/32' diameter though.
Select to expand quoteJolene said..
It's definately an advantage to adjust the rake on the smaller drill bits,, you can also reduce rake by reducing the relief angle aft of the cutting face but that requires grinding the cutting edges down until they are almost level with the trailing edge of the drill cutting face. That angle is commonly about 12 deg but reducing it to about 5 deg helps drastically. You can also put a small flat on that face of the cutting edges. It's easier to do it this way with small drills, bigger drills you are grinding alot of metal away.
Practice on an old drill bit and drill some holes in an old brass fitting of some sort.
All so be mindful that cutting fluid can sometimes lubricate too well and cause tool rubbing and work hardening if you're trying to go too easy especially on a 0 or negatively raked tool. Often a bit of pressure is required to start the cut and keep it going,, the cutting fluid can work against you trying to start the cut.
On a side note, I dislike the new Viper style drill bits with the multi facets. Although they centre nicely and drill beautiful, they lose alot of strength from behind the cutting edges and in a machine shop i have found it's not practical to have that style of point on a drill bit.
Ok great thanks again. I am doing m8.5mm holes tomorrow up to 9mm deep so will do these in 3 steps 4.5/6.5/8.5mm and will adjust the rake on these drills. I won't get into relief angle mods unless necessary - hope it is not necessary. Will do some practice. Noted re cutting fluid.
Those Viper style with the multi facets looks very busy...........ok they might have their benefits but I interpret that an expensive jig is needed to re-sharpen them? For a backyard shed doing this sort of drilling / reaming once in a blue moon they wouldn't add up? As you conclude for your machine shop also.
For information to close this out we have achieved these 6 holes. I didn't need to adjust the drill rakes or relief angle but had to go very slowly and steadily with the depth cut speed as expected.
For some unknown reason I started the holes with 3mm hss drill bit and 5 out of six worked but for one of the two 36mm depth holes the drill broke and the broken end stayed in the casting - a combination of my sloppy efforts and also using a way too small bit. This caused us a huge amount of grief, angst, time and effort to recover from. At brothers down the road with larger bench press than mine we got through the 14mm deep 4 holes to M16 in the gudgeons. 25/32" bit delayed in delivery - my bad for late order. Late that afternoon I drilled into the 36mm depth hole to be from the other side with 4mm drill to try and clear the broken bit but could not.
Went to mate 2hrs up north with home "factory" and drilled out the 14mm deep holes with his even larger drill press and 19mm drill. Lathed them out (put the gudgeons in 4 jaw chuck, boring bar with magic bit, very smooth operator) to perfect fit for the 19.90-19.95mm two 316 pins then tackled the first pintle. Had to take out the lathe bed piece to get enough swing for the pintle - got it all one. Time was getting right away after ~2hrs spent first up early morning trying to roll pinch punch out the broken drill bit.
Mate had 12mm diameter end mill cutter to bore an annular groove around the stuck 3mm drill bit in the 2nd pintle 36mm deep 19.95mm hole needed. I drilled 5 off 4mm drill holes through the annulus made by the mill cutter and broke the drill bit. So now a centre drill bit end stuck and 1 out of 5 periphery drill bits stuck. I flogged the hole with 10mm drill in the press from the rear open side through the 4mm pilot hole, then reduced down to 8.5 and 6, the latter from both sides but didn't get through, and finally cleared the hole including roll punch punching from the original side. Went back up with 6/8.5/10/12/16/19 drill bits then in the lathe and we got the 2nd pintle done. Long work day plus travel each way - enormously well worth it.
From the above the learnings are clear as regards drill size to start. The cutting fluid didn't seem to be needed on the smaller drills but seemed to be useful on larger ones. For all drills the right drill press feed speed needs to be used - slow to start, get the cutting happening suitably then continue at this speed - if too much smoke ease off to avoid work hardening. Great thanks again Jolene for excellent inputs.
