Automate a manual drill press? (for drilling, not milling)

[doorknob]

I've been looking for discussions about automating a manual drill press (via a stepper- or servo motor controlled X/Y table for the workpiece, with a belt drive or direct drive on the quill), but so far I haven't found much.

Most of the threads about CNC'ing a drill press are aimed at turning the DP into a milling machine (or strongly advising against doing so), however that's not my goal. I want to do drilling, not milling.

It occurred to me that one possible approach would be to obtain an X/Y table from a Sieg X2 mill (either the standard one or the bigger one from Little Machine Shop), and doing a CNC conversion on the table exactly as you would do it for the mill. That would leave the quill drive as the remaining problem to solve, but it would probably be possible to find a suitable drive system that has been used successfully on a mill/drill and convert it to work on the DP.

I could probably live with the X2 table size restriction (although it might be nice to have more Y-axis 'headroom' than the X2 tables offer) - in fact, maybe I can even find someone who has a spare X2 table after replacing it with the larger one from LMS - but I wonder whether there might be some other options that people have tried.

I'm also wondering what options might be available for changing drill bits more quickly than removing the old one and inserting the new one using the standard chuck and key.

My DP is the Harbor Freight 39955 "monster"...

Pointers to example DP conversions would be welcomed...

[arizonavideo]

What are you drilling?

[doorknob]

Primarily 6061-T6 aluminum flat bar stock, thicknesses up to perhaps 0.500".

[neutronics]

I used to have a Horror Fright mini-mill, which has a similar head casting to your drill press (with no fine down feed). This is an issue with much coverage in the Yahoo! groups. Some guys put a wormgear on the down feed, some put a Z-axis leadscrew, some put a clamp around the lower bearing housing that held an ACME nut for a leadscrew. Seems like the hardest part of their designs was disengaging the fine down feed to allow manual drilling.

When I converted mine, I used a wormgear purchased from fleaBay and left the stock down feed handle intact. The worm gear was connected to the handle by a “clutch” of sorts, which was released or engaged by a big handwheel. Tightening the handwheel would press the gear face against the handle, loosening the handwheel would disengage it for manual feed.

I don’t have this mill any more otherwise I’d post pics.

[doorknob]

Interesting...

Which Yahoo Group has the discussions about the Z-axis feed mechanisms that you mentioned?

[Geof]

Before doing this conversion think about how accurate the spindle is on a manual drill press. They normally have some sideways slop and rarely does the chuck run nice and true. If you try to start a hole in a flat surface without center punching or in some way precisely locate a starting point, often the drill bit will wander around before biting in so the hole position is off. This does not matter much for manual drilling but if you mount an X Y table so the part can be moved precisely between hole locations, but then have the drill bit wander around each hole location you will get inaccurate hole spacings even though your table motion is precise.

[neutronics]

Originally Posted by doorknob Interesting... Which Yahoo Group has the discussions about the Z-axis feed mechanisms that you mentioned?

http://groups.yahoo.com/group/drillmill/

[doorknob]

Originally Posted by Geof Before doing this conversion think about how accurate the spindle is on a manual drill press. They normally have some sideways slop and rarely does the chuck run nice and true. If you try to start a hole in a flat surface without center punching or in some way precisely locate a starting point, often the drill bit will wander around before biting in so the hole position is off. This does not matter much for manual drilling but if you mount an X Y table so the part can be moved precisely between hole locations, but then have the drill bit wander around each hole location you will get inaccurate hole spacings even though your table motion is precise.

I recently used a Bridgeport clone (made by Victor) using an Accu-Rite Millpwr controller (to handle X- and Y-axis table positioning) to fabricate some aluminum brackets out of 0.500" thick bar stock. I needed to drill 8 holes with an X bit (.397" dia) and another dozen holes with an H bit (.266" dia).

Even with a Bridgeport-class mill and its hefty spindle and quill, I thought that it would be prudent to first use a stiff, #3 center drill to make shallow holes in all of the hole locations. Then I drilled all of the locations with the H bit. Finally, I used the X bit to drill those holes (effectively using an H-sized hole as a pilot hole for the X bit).

Was I being overly conservative in drilling that way on the Bridgeport? Or is that a recommended way to drill such holes even with a stiff milling machine?

Why wouldn't such a technique also serve me well with an automated drill press?

(I'm pretty new at this, having had only a few short hours of experience using a Bridgeport mill)

[ger21]

There was a member here several years ago that had I think 2 CNC drill presses, and had some threads here on them. Unfortunately, he passed away a few years ago, and all the images in his threads disappeared, as they were linked to other sites. His user name was Stevie. He had a lot of threads here, but I don't think any of the pics have survived.

[Geof]

Originally Posted by doorknob ......Was I being overly conservative in drilling that way on the Bridgeport? Or is that a recommended way to drill such holes even with a stiff milling machine? Why wouldn't such a technique also serve me well with an automated drill press? (I'm pretty new at this, having had only a few short hours of experience using a Bridgeport mill)

If your 0.397" holes were to take 3/8" bolts you were possibly being overly conservative because you had plenty of clearance. However spotting the holes is good practice simply because drill bits rarely run really true so when they start into the surface they nearly always start a little distance away from the trues center and then just deflect and drill in that spot.

On a nice stiff milling machine your spotting drill if it is held in a good collet, is probably going to run very true so it will spot quite precisely on center, but a drill press is not stiff and in an ordinary drill chuck the spotting drill may not be running nice and true so when it touches down it starts the hole off center. Then the sloppy spindle just deflects and spots the hole at the out of true location.

I am maybe being too conservative because the deflection will probably not be greater than your 0.022" difference between the hole and bolt diameters, but if you tried drilling and reaming precisely located dowel pin holes you would probably find it inadequate.

Incidentally you don't really need a pilot hole for the X bit especially if you use drills with a split point grind.

[doorknob]

Yes, the 0.397" holes were meant to provide clearance for the threads of 3/8"-16 bolts.

The drilling that I am likely to be doing with this machine will be of the same general order, along with some drilling of holes that are later to be tapped (manually, or possibly with a tapping head - I'm not sure whether I could also successfully automate the use of a Tapmatic or similar head).

I would like to achieve a decent level of position, diameter, and circularity accuracy as well as repeatability. I'm not yet certain how to translate that into just how many thousandths of tolerance would be considered 'acceptable'.

This discussion is quite helpful, thanks...

[arizonavideo]

If you will be doing a large # of holes it might be worth it to look at finding a used RF-31 mill. I have one and it is old and beat but it is a great drill press and will hold way better than .022" between holes. The long 5" quill is still tight in my Taiwan version of the machine. The China ones will have more slop in the quill.

You just cant beat it for a drill press and used one with a bit of rust might go for $300 to $400.

The one I have is extra but I'm in Phoenix.