Swaggie
SubscriberI have today had made up a longer towball mount for my camper trailer to allow opening the D2 rear door to clear my newly made winch mount to close the hard floor camper.
I bought a 330MM towbar mount but the only type available has about a 150MM "drop" compared to the original 30MM drop which is just about perfect. So I cut apart my 30mm drop receiver and had a trailer manufacturer certified welder weld a blank bit of 50MM square tube onto the original head.
I redrilled the pin hole in the 330 MM to 290MM ( vs 220 before) which allowed the door to Just clear the mount with an old 11/16 stepped bit that I have had for 20 years which I did in stages , as the old bit is pretty blunt and it took a lot of time and brute force and chattering to do it.
So I went and bought a new 11/16 drill which is not easy as Bunnings and Masters skip from 16 to 18MM and don't have 11/16. It is a Chinese Atlas.
Now my question is whether it is better for the drill bit to do the hole in one go or to do it in stages like 5MM, 10MM, 13mm and 11/16. I have Bosch cutting oil. The drill is a cheapo 600watt ALDI bench drill.
Any advice appreciated as I wonder whether doing it in stages tends to blunt the outside portion of the drill.
Regards Philip A
Last edited by TerryO; 20th November 2014 at 09:10 PM. Reason: Move to Tool Time
Swaggie
Hi Phillip,
If using cutting oil, a sensible rotational speed and pressure (feed) to suit the bit diameter in use then stages are always better. Only a few are required, the ability for the bit to cut more at the face than the shoulder is preferrable.
JC
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Super Moderator
Drill a 10 mm guide hole.
If you don't like trucks, stop buying stuff.
RoverLord
Measure the center of the bit where the two cutting faces meet, your minimum pilot hole should be no smaller than that, the maximum should be no more than about 2/3 of the drill bits diamter or you will increase the chance of chattering or chipping the outside of the cutting edges off.
Dave
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Swaggie
The pilot drill should be larger in diameter than the chisel point of the next drill. If you only have a feeble bench drill with insufficient power to drive the 11/16" drill in one pass then I would drill in three steps. 11/16" is a standard size. I can't understand why the size is hard to find. Cutting speed for HSS tools in mild steel is 9000/diameter in mm.
URSUSMAJOR
Master
SubscriberWhat he ^^ said......
1/4 - 5/16 pilot, then 11/16. Moderate speed, coolant and keep moderate pressure on the bit.
Wizard
Philip
Unless the entire modification has an Engineers Certificate you will be accepting full liability if it happens to fail.
Having a certified welder complete a portion of the work does not impart liability to the welder. The welder can certify the weld that has been done, but not the (your) intended purpose of the entire arrangement.
Regards
Andrew
Fossicker
Much better to use a rotabroach than twist drills for that kind of work.
Swaggie
SubscriberThanks to everyone who responded.
Regards Philip A
Phillip, extending your tow hitch by that much will have greatly reduced its rated towing capacity / ball weight...
Best get it checked mate..
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