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Old 08-10-2018, 08:56 AM
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Draker Draker is offline
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Default Unibit RPM speed

Are there guidelines about the correct RPM speed to use when drilling aluminum with a step bit (unibit)? Reading threads here I’ve seen both “use high RPM” and “use low RPM” recommendations. I ask because I’ve had mixed success with this tool in the past, using a drill press to drill the conduit holes in the wing ribs. I’ll be drilling through the main center section soon and want to do it right. Also, lubrication or no lubrication? High or low drilling pressure?
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Old 08-10-2018, 09:08 AM
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JonJay JonJay is offline
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Generally speaking slower speeds allow for better control. However, I doubt your issues are with speed. Most get poor results in thin sheet by not supporting the work. I use a wood block under the web to support the sheet and drill right into the block as I make the hole.
If you don't support the web it can flex and bind which can cause inconsistent results.
My guess is you will have much better luck on the thicker center section.
Lubrication isn't always necessary in a non production environment (we typically are not cutting at max work speeds) but it cuts down on tooling wear and certainly won't hurt.
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Old 08-10-2018, 09:12 AM
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BoilermakerRV BoilermakerRV is offline
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Default Free Opinion

I have had the best luck just using a cordless drill and pretty slow speeds. I start of with a little extra pressure, but once the step starts cutting I back off the pressure and maybe increase the speed a bit. As the step reaches the far side of the sheet, I back the pressure to near zero.

I also use a Sharpie to highlight the desired step, so I don't get carried away. Overall, I have found these tools to be quite handy and make some very nice looking, clean holes. They are prone to "walking" when using the cordless drill, so if the location of the hole is critical, take extra precautions.

Good luck!
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Old 08-10-2018, 09:22 AM
rocketman1988 rocketman1988 is online now
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Default Support

Support is the key. Also, as the diameter of the hole increases, the rpm should decrease.

Put a 2x4 under the work piece and drill into it. Be aware of hoe you set up the work and table as many units will be long enough to go through the 2x4 and into your drill press table...
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Old 08-10-2018, 11:06 AM
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Paddy Paddy is offline
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Default Tool Speed

The question of tool speed is a good one for working with aluminum, especially for larger holes associated with a unibit. See below link for a handy calculator to convert RPM to linear cutting speed.
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Old 08-10-2018, 11:54 AM
ksdflying ksdflying is offline
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Location: Antioch, Tennessee
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Great post. I've had struggles too. I second the tips on here. For me, using it in my cordless hand drill, was the marked improvement.
About the lube, I insist yes, use BoeLube on this and everything. I am a huge believer now as I have seen an eye opening marked improvement on drill bit and reamer tool life. Not only life, but I've seen again marked improvement on cutting surface finish. Lube is a must for sure.
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Old 08-24-2018, 03:47 PM
lr172 lr172 is offline
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a general rule of thumb is to use slow speeds and extra pressure for steel and higher speeds with moderate pressure for aluminum.

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Last edited by lr172 : 08-25-2018 at 07:45 AM.
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Old 08-24-2018, 05:52 PM
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Greg Arehart Greg Arehart is offline
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Sometimes helps to get a clean hole if you do the last part of the last step from the back side.
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Old 08-25-2018, 03:24 AM
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Major-Tom Major-Tom is offline
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I use styrofoam to support the part while drilling. This has the same result as a wood block but it is easier.
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Old 08-25-2018, 05:30 AM
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uk_figs uk_figs is offline
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Default screwdriver

I have had the best outcome on thin metal using the unibit in a battery powered screwdriver, slow speed and easy to control, also as mentioned above if you can finish the hole from the backside.
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