Drilling Cylinder Head Bolts

[tux]

I need to drill some Torx cylinder bolts with 1.5mm holes for a wire seal on my Autograss car. I bought some drill bits, used a slow speed and a spray of good old WD40 to lubricate, but they appear to be made of purest "undrillium." I expected them to be hardened steel and difficult, but this is something else.
Am I missing something, or are they really going to be that hard?
If I go to buy new drill bits, which would be better, titanium coated or cobalt?
Cheers
Pete

 

[pedrobedro]

You shouldn't run 1.5mm drill bits on a slow speed.

 

[scott0031]

They wont be hard, they will be tough. As mentioned silly slow speeds wont get you anywhere fast, probably the bare min speed you should try is 500 rpm a rough guess if the material is that tough, you also don't want it screaming at 3000 rpm as you will get a lot of heat generation and risk the high speed of the drill depositing in the hole and making it all go a bit wrong. Speed is really dependent on several factors that you only really get with experience knowing what it will take and what works.

You really should have no problems drilling a high tensile steel.

Some questions first to help you resolve the problem.

What drills did you buy?
Is the geometry correct on the drills, (a lot of cheap drills are incorrectly ground)
what are you trying to drill it with?



Kind regards,


Scott

 

[hotrodder]

I wouldn't go out of your way to buy Ti nitride coated- take a set of Dormers for example and below 2.0mm they'll be uncoated...
Cobalt drills are more difficult to blunt/kill with heat but easier to snap...

As said small dia drills need higher rpm regardless, a cutting speed of 30 sfm is around 1800 rpm for a 1.5mm drill but as Scott said there are other factors. Putting a very small flat on the side of the bolt head with a grinder can help, especially if the heads are case hardened

 

[graffian]

I used to buy cotter pin drills for drilling bolt heads. I haven't ever worked out cutting speeds;-) I run a 1/16" cotter pin drill around 2000 rpm.

 

[tux]

Thanks guys. Based on that I suspect that the drill bits are a bit gash. They are "Acme" drills from the local DIY shed and, while I expected them to be poor, I thought 3 of them might actually drill one hole!
I'll see if I can get some better quality drill bits.

 

[brightspark]

just buy a few decent high speed drills from cromwells . dormer. presto guhring .as said medium speed use cutting compound and a decent feed pressure

 

[john224]

Try using a (( tungstone tip)) DRILL BIT brick drill on slow speed this is what i used to use at work when drilling hardend steel to remove broken taps and drills when making machine tools,, just have to take your time though,,

 

[ronan]

+1 on the cobalt drills , they will cut when a normal drill would be long blunted.

 

[dai]

+1 on the cobalt drills , they will cut when a normal drill would be long blunted.

+2

 

[tux]

Thanks all. I've ordered up a couple of cobalt drills to try.
I've actually found a bit of a "loophole" that allows me to drill the head and cambox instead, which are both ally, so job done anyway.

 

[Cris B]

From experience, another vote for the Cobalt bits - there are some sellers on eBay that will sell a box of 10 for a good price which is well worth it as these bits are quite fragile - I have also found that proper cutting oil makes all the difference in comaprison to things like WD40.

 

[ronan]

Try some trefolex , smelly green paste that i have used for years and swear by , made in manchester too .

 

[NeilH]

any cutting oil is better than none.

i like Temaxol.