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| Arnak:
Hi Folks, Just in case anyone is interested in my pillar drill mod. It is one of the cheap drills for fixing to a bench. What I needed was a drill capable of using my tapping head but the depth was too short and the lowest speed, about 350rpm was too fast. The first thing to do was to increase the length of the pillar by adding a suitable diameter of steel rod with the lower end reduced to fit into the existing hollow pillar. I was going to pin it in place but the fit was so tight I was able to press it in. Having increased the throat size I then needed to reduce the speed. I managed that by adding some support steel strips to move the motor out far enough to add another shop made 2” pulley onto the motor shaft. I used one of the stepped pulleys in its original place by adding a cross plate to hold a bearing holder with a bearing at the top and the bottom of the steel holder. That holder is in slotted holes to allow for adjustment. The position of the motor was set by the length of the belt I could obtain, just 1” below the original belt length. I think that the pictures are self explanatory but if anyone needs more detail please ask. Arnak |
| Stilldrillin:
Nicely Modded, Arnac! :clap: :clap: I need a similar belt mod to my mini mill. The revs are much too high for my purpose. :scratch: Well done! :thumbup: David D |
| Arnak:
Hi David, I'm glad the info was of some use. At least it is a cheap and cheerful way of lowering the speed. You could of course make a new stepped pulley for the motor shaft to give more speed variation. :thumbup: Arnak |
| Steam Geek:
How did you calculate the rpm to get the correct pulley sizing ? |
| Arnak:
Hi, Steam Geek, Actually I didn't as all I wanted was toi get the drill to go as slow as possible from it's lowest speed which I think was about 500rpm. Given that the smallest pulley on the compound original pulleys was about 2.25" I had to settle for that, any smaller and the belt may not have gripped properly. You could try a bit smaller and see if it works, the ratio calculation is I believe driver dia divided by the driven dia. So the ratio of 2" to a 1" pulleys is 2 to 1, if the 1" is rotating at 1000rpm the 2" will be rotating at 500rpm. That is the first step in the chain of drives, so once you have the speed of the intermediate pulley you make the same calculation with the intermediate pulley and the next one in the chain. I hope that makes sense? Come back if you need more help. Arnak |
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