VFD recommendations sought

[snip]

I looked at it this morning. It's a long shaft (~6 inches) with a long keyway, plus two circlip grooves between which the variable pulley mechanism sits, all metric. Definitely custom.

In another posting, Gunnar suggested machining an adapter shaft, which could be done, but I don't know that I want to go to the trouble.

Instead, I'm thinking of getting a VFD that's big enough to run this little 1/3 HP motor off one phase when I'm using the little drill press, and this same VFD to run a larger 3-phase (probably a floor model) drill press to be named.

The other issue that's developing in the DP350 is belt wear. The inside of the housing has a layer of rubber dust already, and I've only had the unit since 29 April 2005. I recall some complaints on Amazon about the belts wearing out too fast, and some people saying that they had not had that problem. I suspect that the cause is the sharp edges on the inside of the pulley cones, where the facing cones mesh. The belt is perpendicular to and runs over these sharp edges; this cannot be a good idea. I plan to take the drive apart and round those edges with a hand file. The cones are made of zinc-aluminum die metal.

The belts cost $38 from Delta; while $38 seems a bit much for a belt, I did buy one, to have a backup. What Delta provides is a Tru-Power V13x860.

This was my instinct, but I'm glad to hear confirmation.

The other problem I'm having is large drill bits and countersinks slipping in the chuck. With the original keyed jacobs-style chuck, it was not possible to get it tight enough by hand, so I used a six-inch length of 3/8 black iron pipe as a key extender. This does work, although the key arms were right at the edge of bending, or a little bit over the edge, and the whole operation was pretty time consuming.

So, I bought a Phase II keyless 1-13mm chuck (Travers # 63-099-024, $32) and it's a lot faster, but it too will slip on the larger stuff. I got a surplus spanner wrench that allows me to hold the top (narrow) knurled ring while hand tightening the body of the chuck, and this works for all but the MA Ford 5/8 inch countersink (which has a very smooth shank). There is noticeable added tightening when using the spanner.

I think I'll roughen the shank of the MA Ford countersink with flooded wet-dry sandpaper. It really doesn't need to be polished.

I'm wondering if a better chuck would help. I looked at the ball-bearing jacobs-style chucks, and at the more expensive keyless chucks, such as those made by Rohm. Any opinions?

Yes, but I gather that you have direct experience with this setup, and it works as one might expect and hope that it would. Said another way, there were no surprises. This is often the key.

Joe Gwinn

[ ... ]

Hmm ... you *do* know that *single* phase induction motors do not start well (if at all) at anything other than their nominal frequency? Typically, a 60 Hz motor can be started on 50 Hz and vice versa, but run the frequency much up or down from there and you will have problems. (A cap start motor could benefit from changing the cap value depending on the frequency, but I'm not at all sure that it will have much torque in any case.) I don't think that you can make this usable at all. You won't have enough speed range to do you much good, and you will always have to start it at the nominal frequency and then adjust to what you want and see whether the motor stalls before you even put any load on it.

[ ... ]

Note that Albrecht makes a keyless chuck with diamond impregnated jaws, so they will grip on a hardened shank. I'm not sure that you can find those with Jacobs taper sockets for an arbor for your drill press. I think that they may be only in the "integral shank" line, where you can get them with R8 shanks, or NMTB 30 or 40 or 50 shanks to go right into your milling machine.

Good Luck, DoN.

I suspected there would be a problem, but can't say that I knew it. This is why I tried the idea out on the group. At this point I'm collecting ideas. And if I go the VFD with 3-phase motor approach to variable speed, it won't cost me much to try it out on the little

1-phase drill press. I probably only need to be able to run at say 1/2 speed, and could have a run capacitor sized for 30 Hz.

So far, torque has not been the problem. If anything, the problem has been that the chuck doesn't pinch the tool shanks nearly tightly enough, so the chuck slips rather than the motor stalling or even laboring.

It's a J33 taper, and Albrecht does make a diamond-impregnated keyless chuck to fit (Travers # 63-005-558 for instance), and I've got to believe that it would work well. But I'd feel a bit silly putting a $326 chuck on a $200 drill press.

There is a pecking order of cost and value, and I'm trying to find something a bit better than what I have. Any ideas?

No milling machine yet, for lack of a place to put it. Likewise lathe. But soon. I'm slowly building my shop up, often on the debris of what was once a vibrant machine-tool and manufacturing industrial base in New England. Also, judging by what turns up on the used tool market, there must be a lot of mechanics retiring and selling their tools by the pound.

Joe Gwinn

Well ... try paralleling a second start capacitor of the same value with the original one. This will only help with starting, however, and I suspect that the torque needed to stop the spindle will still be lower than you would like.

[ ... ]

I can understand that.

Hmm ... Can you find an ER collet adaptor with a MT shank to fit your drill press? That, and a few selected collets might do the job for you.

An alternative might be to simply get the tools you need with a Morse taper shank to fit the drill press. I'm not sure whether a Ford countersink is available with a MT shank, but you could check for it. You might even call a good vendor like MSC (if you don't find it in their catalog) and ask them. I've had them call the manufacturers for a special at times -- and it wasn't *too* expensive. (I needed a non-standard set of chasers for a Geometric die head for my turret lathe.)

I know that for larger drill bits, I use MT shanks directly in my drill press. (Though I've not had any problems with slipping chucks in that one. It is a MT-2 spindle, with a Jacobs keyless chuck (akin to the Albrecht in design and behavior). Granted, I did not pay new price for that chuck, but lucked into a barely used one. I only had to get a good arbor to fit my drill press spindle. Most of my other drill chucks are Albrecht, with one Rohm (3/8" and quite good) and one Polish made clone of an Albrecht (not as nice) in my bigger (12" swing) lathe Tailstock. The key type Jacobs chucks are a real pain in a lot of situations.

Good Luck with that, DoN.

That's a good idea.

Running at half frequency (30 Hz versus 60 Hz) requires that the drive voltage also be cut in half, to maintain constant flux density within the motor. I don't think the running speed regulation is greatly affected, but I suspect that the breakdown torque (where the motor stalls) is cut in half compared to what it would have been had the motor been wound for 30 Hz. The answer is probably documented in application notes somewhere.

So the question will probably be how close to breakdown torque we are at present. The mechanical variable-speed system drops the speed to 536 rpm for a motor speed of 1750 rpm, a 3.26:1 ratio. (These are measured values, at zero load.) The torque at the chuck will increase by a like ratio, and I have not seen the motor even laboring.

For the record, the ad copy claims 500 rpm to 3100 rpm, and I measure

536 to 2948 rpm (no load), so the ad copy is a bit optimistic. The motor turns at about 1750 rpm, at the motor shaft.

[snip]

This is something to consider when I get the floor mount drill press, but the cute little Delta DP350 has only the JT33 taper. I like the size of the DP350 for many things, but in retrospect I'm not sure the mechanical variable speed was that good an idea, although it sure is convenient.

It pays to be lucky. So, the Rohm chucks are good. That's useful to know. I assume you mean the Rohm keyless chuck. While the ball bearing keyed chucks are better, they are still keyed.

Thanks. I used to have access to a small machine shop and lived in apartments. Now I have a wife and a house (now with a small workshop area), but too far away from that machine shop. So, I'm seriously short of iron toys, and a lot has changed over the years. At least the wife doesn't mind the iron toys, even the noisy ones. But I don't think I'll start a foundry operation.

Joe Gwinn