ARO Drills modified for ShopBot use

[Gary Campbell]

I finally got time to shoot some video of these drills working. They have been mounted for a few months and I have received a couple dozen emails about them. I will give an explanation of the hows and why's.

Let me first state that this is not neccessarily a way to save a few bucks versus buying the ShopBot Drill system for your PRS. At $1,700 retail new, plus a few hundred more for valving, wires, tubing and fittings, you could easily spend LOTS more than the PRS drill costs. (Especially if you buy a used one that needs rebuilding and revalving as I did) You may be able to find them used for a good price, but there are about a hundred rpm and valving options, so be careful. They are a very good solution for shops with smaller compressors and drill very clean holes, due to the adjustability. You can notice in the videos that the 8mm drill plunges much slower than the 5. This keep the hole quality very good.

Drills were mounted on shop built aluminum brackets to the OEM spindle plates.
A 1 1/4" Delrin mounting block was used to mount the drill to the brackets.
Prox and rare earth magnets were added so that full hole depth can be confirmed prior to gantry movement.
Both plunge and retract speeds are adjustable on the fly for varying material density.
Drills have RPM range from 500 to 17,000 rpm and HP from 1/6 to 1/2

Here is a pic of them mounted on my gantry:


370

And here is a link to a video of them drilling: http://www.youtube.com/watch?v=fk_zWioyvQs

And another showing them working without the vacuum noise. This allows you to hear drill action and compressor use, as it actually starts up and then stops during drilling. http://www.youtube.com/watch?v=Tr5TvVV5YNE&feature=channel

Gary

[bill_lumley]

Gary , thanks for sharing . I am very interested in this topic as I am trying to solve the problem of my compressor(60 gallon 3hP) not keeping up with the PRS air drill and at the same time increase drilling speed without compromising hole quality . At the moment I only drill 5mm holes for system holes and hinge/drawing mounting hardware . I am about to split my air circuit in two so that I can control the plunge seperately from the drilling action to be sure the drill is not running continuously . Getting special air control parts from the US is a hassle so I am just using ball valves at the moment to facilitate the splitting of the functions to confirm it works OK but I am wondering if the relatively slow speed of the air drill (2500 RPM) is what limits my drilling speed and hole quality so I am thinking the next step is the air grinder mounted in a bracket similar to what you show becuase I can use router bits to drill at router speeds . It appears the unit you show here accomplishes the plunge and drill in the same unit . Is that correct . Why did you go with a unit like this over the die grinder that you mentioned in another thread ? At the moment I have to limit the drill Z plunge rate to under 2 in/sec. with asolid carbide boaring bit to ensure I get a reasonably clean hole.

Thanks Bill

[Gary Campbell]

Bill...
Get with Nat Wheatley as he has a good working setup for the PRS drill. I helped him work out a couple of the details of the electro-pneumatics to get his working. He also has modded the postP's to make it all work.

Most air drills use between 2 and 4 cu. ft. per drill cycle. The ARO's claim 2.3 cu ft. At around 16 to 18 8mm holes per minute that is an air use of close to 45 cfm. My 7.5 hp compressor just keeps up, your 3hp will struggle, unless you have a lot of travel in your files. The plunge is a lot quicker on the 5mm drill so it uses much less air.

Just like anything else in the cutting world your drilling plunge speed is a product of PRM, move speed (plunge) and bit type. I was never able to get good quality at a speed anywhere near 2ips. The drills in the video have a 3" stroke, time how long they take to plunge.

I have a end grain doweling video on my page that shows dowel drilling with an 8mm bit in the spindle. That bit plunges at 2ips @ 12K rpm. You will need at least 10K to plunge that fast. Make sure that the bit is rated for that rpm.

Keep after it... you will get it.
Gary

[bill_lumley]

Yes I am in touch with Nat and he has been helpfull . I am following his method to see where it takes me . It only has to improve over where I am now

[Gary Campbell]

Bill...
There are many ways to skin the proverbial cat. Get your drill cycle working as Nat does... if that doesnt get your air use so that your compressor can handle it, let me know... I have a couple more tricks for you.
Gary

[bill_lumley]

Gary , with Nat's help I got the drill cycle working properly using some ball valves to control the drill thrust but it appears the cold that my shopbot is in makes it difficult to run it on compressed air even though I have my compressor in a warm location feeding it . The garage where my bot is was -10C today and the drill while plunging was intermittent . I talked to the folks at Shopbot and there seem to be several issues dealing with cold tools and compressed air that make it very difficult to get a reliable air drill working in this climate . Unless you have tricks for climate I think I need to turn my attention to getting a die grinder solution working in place of the actual air drill . This removes the dependancy on weather conditions . I want to heat the space eventually but that is several months away .

Bill

[Gary Campbell]

Bill...
The only cold climate tricks I know of (after living in the UP of MI) is to get out on the road and drive south til its warm!

We used to run into that problem with air tools in the north. The warm (humid) air freezes in the tools as the vapor condenses, rendering them inoperable. We used to use oilers with ethylene glcol in them. I do not reccommend this for your drill tho.

Can you mount a die grinder to the slide the drill is mounted on? I have only seen pics of the PRS drill, never in person.

Gary

[bill_lumley]

Gary, I got a nice die grinder today that has variable speed and an offset spindle that should work fine - It has a low speed range compatible with drilling speeds . I can't mount the grinder using the bracket that comes with the drill . I have to find a metal worker to build a new bracket to mount the grinder on the exisitng slide and turn the slide around to face away from the spindle . The current bracket has the slide facing the spindle and there is not enough space for the grinder to fit . The grinder is about 1" wider than the air drill .

This is the air grinder I found locally that looks well suited to the job .
www.jwalter.ca/walter_ca/servlet/ProdSearch?franchise_id=PT&item=30A145 (http://www.jwalter.ca/walter_ca/servlet/ProdSearch?franchise_id=PT&item=30A145)

Before putting a lot of effort into it though I need to confirm the specs of the air cylinder with Shopbot as the manufacturers web site has thousands of products and not all are suitable to operation in cold temperatures.

I understand now why people go south for the winter


Shopbot is pushing my knowledge further again . I have never had to deal with pnuematics before .

[Gary Campbell]

Bill...
Send me an email, I may be able to get you aimed in the right direction. You have the option to park the new tool below the z and plunge with the Z axis as the PRS drill does, or plunge with air. either takes the same effort.

You can get some good ideas from Jim Harmon's brackets and clamps in this post: http://www.talkshopbot.com/forum/messages/312/33467.html?1219789836

Good Luck, Gary