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View Full Version : determine rpm with dc or vfd



lowcountrycamo
05-21-2012, 01:01 AM
I am getting much vibration on my atlas 12 coming from jack shaft and motor. Thinking of converting to dc/control or 3 phase/vfd. For those of you that run either, how do you judge/measure rpm. I assume you could go by quality of cut but a tach would be better for overall tool life right?

flylo
05-21-2012, 01:12 AM
I use lazor tach. Ihave one I paid 20+ at HF & a small one from ebay for under $12. You cut a tiny pc of reflectic tape & stick it on what you want to test aim the tool & pressthe button. Both are pretty accurate.
I borrowed this next idea from a members website. I ordered sever bicycle speedometers for under $5 ea/delv. You need the 2 button type because it has the RPM function. I plan on putting one on each lathe,mill & any other variable speed tool I have.

lakeside53
05-21-2012, 01:14 AM
On many VFD (Hitachi for example) you simply insert a constant into a register that represents a frequency multiplier for the display. The display now reads RPM. You can also read the 0-10v (or whatever) output with a dvm module, and even have a simple resistor network switched to indicate which gear/belt is in use.

or.. you just put a scale under the variable speed knob, and put as many scales as you need for belts/gears.

Oh, you can add (or use an optical) a tach...

Highpower
05-21-2012, 01:22 AM
I use a "Tachulator". Displays RPM or SFM.

http://img.photobucket.com/albums/v82/Highpwr/Lathe%20conversion/th_VFDandtachulatorpanels.jpg (http://smg.photobucket.com/albums/v82/Highpwr/Lathe%20conversion/?action=view&current=VFDandtachulatorpanels.jpg)

lowcountrycamo
05-21-2012, 01:55 AM
all good ideas... Thanks!

bytewise
05-21-2012, 10:34 AM
I have a 9 in Atlas and had more vibration than I liked at high speeds. I took things apart and found several pulleys and chuck badly out of balance. I rebalanced each major part seperatly. After the work, the machine runs well at the highest speed.
Hugh

metalmagpie
05-21-2012, 02:02 PM
Lots of times you can balance cheap sheaves simply by machining the back side. Not that you'd do this on your Atlas, but I used to buy the cheap zinc pulleys and true them up on my lathe and after that they weren't too bad.

I've always thought that belt/pulley systems can be made to run smoothly, but you often have to put a lot of work into it.

Start by removing all the belts and see if your motor vibrates by itself. If so, work on that first. Once you get your motor silky smooth then put on its belt and run just that one. If the system now vibrates then machine/balance/align both pulleys until all runs smooth. Keep on that way and by the time all your belts are on your whole machine should be smooth.

You *can* take small motors (less than 5hp) and get them precision balanced. Bring about $150.

metalmagpie

gzig5
05-21-2012, 06:35 PM
Look into Fenner Link Belts
http://www.fennerdrives.com/high_performance_composite_vbelts/powertwist_home.aspx

There are other knock offs as well. You may have issues with your pulleys, but a crappy belt will produce a lot of vibration as well. I use Link Belts on my Craftsman 12x36 and even though the pulleys don't all run true, the machine is smooth at high rpm.

Lots of ways to skin the speed read out cat. What you ultimately want to know for feed and depth of cut is the surface speed of the work, which is rpm x diameter at the cut.