Rock drill basics | TreasureNet.com

I have an APT 155 rock drill i bought second hand. I have some brand new Brunner and Lay bits. (button and cross carbide 1.5”)
I am trying to drill what we call “blue granite” here in Northern ca. Its a VERY tough rock that is almost navy blue with small white quartz specks.

With my drill on full blast, with a brand new button bit as recomended by B&L for hard rock, i got maybe 2” in 30minutes.

It seems like maybe the drill is not hammering as hard as it should? It spins fine, but its just not pulverizing the material.

I can get one hole 20” deep with a 10mm sds plus bit in about 10
mins. The bit is usually toast after 2 holes, sometimes just one…

Anyone with experience drilling rock that appears to be 8 mohs

I just gotta say, the Egyptians must have had some advanced tech because theres no way in heck they quarried stone like this with pounding stones- no way.

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You gotta put all your weight on those sinker drills, especially with button bits. If its bouncing your sacrificing a good penetration rate. Bouncing is also harmful on your bits and steel. Anyhoo, high compressive strength rock has always had it issues and if the rock is rather soft that has its issues also. I'd maybe try the cross bit just to see how they do, because that design seems to chisel out better with less feed force imo and not ever driller weighs 200 plus pounds. These are things I've learned as a hardrock miner and a buyer for Yenter blasting in the early 90s and back then they had crews running sinkers ever working day. None of the sinker drillers gave me a good opinion of the button bits I bought to try out and told me get no more of those, so back to deep insert HD H-Thread bits we went. I worked for B&L in the past for 7 years as a rep in AZ, NM, UT, NV and CO and have sold their products as a dealer for now 30 plus years. Still your drill might need a refreshing with new pawls, seals and possibly other things. I can send you a PM with a contact of a partner of mine who can talk through some of the issues you're concerned over. He's herd of so many issues with pneumatic rockdrills over all the years he's been dealing with sinkers and jacklegs. I can say one thing is you wanna keep those side rod nuts good and tight. Also that could be a sign of what's called a cushion bushing that needs replaced. It's a bushing that cushions the hammer or piston impact on the front end and when that passes air it puts a lot of stress on your siderods and breaks them.

I have an APT 155 rock drill i bought second hand. I have some brand new Brunner and Lay bits. (button and cross carbide 1.5”)
I am trying to drill what we call “blue granite” here in Northern ca. Its a VERY tough rock that is almost navy blue with small white quartz specks.

With my drill on full blast, with a brand new button bit as recomended by B&L for hard rock, i got maybe 2” in 30minutes.

It seems like maybe the drill is not hammering as hard as it should? It spins fine, but its just not pulverizing the material.

I can get one hole 20” deep with a 10mm sds plus bit in about 10
mins. The bit is usually toast after 2 holes, sometimes just one…

Anyone with experience drilling rock that appears to be 8 mohs

I just gotta say, the Egyptians must have had some advanced tech because theres no way in heck they quarried stone like this with pounding stones- no way.

Start with a pilot hole to create a guide for the larger drill bit.
Apply steady, even pressure and use a slow, controlled drilling speed to prevent the drill bit from overheating or binding.
Use water as a coolant and lubricant to keep the drill bit and the granite cool during the drilling process.

Start with a pilot hole to create a guide for the larger drill bit.
Apply steady, even pressure and use a slow, controlled drilling speed to prevent the drill bit from overheating or binding.
Use water as a coolant and lubricant to keep the drill bit and the granite cool during the drilling process.

He doesn't need to drill a smaller pilot hole and most sinkers drill dry. The most effective way is start with a series. Start the hole with a larger bit and short 2' rod. Then pull out that rod and add a 4' steel with the next smaller diameter bit and drill that to a 4' depth and then pull it out and add the smaller diameter bit with the 6' length rod. All the manufacturers all try to push their single pass bit, as all you need, but back in the day 40+ years ago all the contractors running sinkers ran with a series of bits and steel. If I was paying for the drilling accessories that's the way I'd do it, because your bits and steel last so much longer. thank you all for the replies!

also, yes any info on where/who/ how repairs a APT drills would be appreciated. I contacted APT and they said the only option in my area for repairs is United rentals. I also neglected to mention that I don’t have an inline oiler, and that oil starts to shoot out the filler cap. Even if it’s clamped tightly on the drill body gets very hot after about 10 minutes of use.

You gotta put all your weight on those sinker drills, especially with button bits. If its bouncing your sacrificing a good penetration rate. Bouncing is also harmful on your bits and steel. Anyhoo, high compressive strength rock has always had it issues and if the rock is rather soft that has its issues also. I'd maybe try the cross bit just to see how they do, because that design seems to chisel out better with less feed force imo and not ever driller weighs 200 plus pounds. These are things I've learned as a hardrock miner and a buyer for Yenter blasting in the early 90s and back then they had crews running sinkers ever working day. None of the sinker drillers gave me a good opinion of the button bits I bought to try out and told me get no more of those, so back to deep insert HD H-Thread bits we went. I worked for B&L in the past for 7 years as a rep in AZ, NM, UT, NV and CO and have sold their products as a dealer for now 30 plus years. Still your drill might need a refreshing with new pawls, seals and possibly other things. I can send you a PM with a contact of a partner of mine who can talk through some of the issues you're concerned over. He's herd of so many issues with pneumatic rockdrills over all the years he's been dealing with sinkers and jacklegs. I can say one thing is you wanna keep those side rod nuts good and tight. Also that could be a sign of what's called a cushion bushing that needs replaced. It's a bushing that cushions the hammer or piston impact on the front end and when that passes air it puts a lot of stress on your siderods and breaks them.