VFD and DRO

[AccelR8]

I have a lathe which was converted to VFD several years ago. Actually I had a company build me the entire conversion package with all the components and wiring completed, I simply had to install it. So in other words, I don't know all the finer details of the conversion package. It just works, which is what I was after.

I find myself using it more and more lately and I've been wanting to install a DRO. I notice, however, when the machine is running if I lay a digital caliper anywhere on it the caliper gets scrambled, a six inch caliper will read something like 23 inches for example, and has to be re-zeroed before use. I never noticed this before the conversion. No biggie but I wonder if I'm going to have issues with a DRO.

Are there different DRO scales? Magnetic, optical, etc? Just beginning to research this...

 

[Ledd Slinger]

Yeah you can have issues with certain types of DROs due to electromagnetic interference but that should only happen if you are running sensor wires next to power wires.

Grounding is very important on precision machinery with motors controlled by VFDs. Ensuring your machine has a solid ground to earth (especially on the frame of any AC motor) will help dissipate any transient voltages from the frame. Also check for proper grounding on the main power system supplying the shop.

 

[AccelR8]

Yeah you can have issues with certain types of DROs due to electromagnetic interference but that should only happen if you are running sensor wires next to power wires.

Grounding is very important on precision machinery with motors controlled by VFDs. Ensuring your machine has a solid ground to earth (especially on the frame of any AC motor) will help dissipate any transient voltages from the frame. Also check for proper grounding on the main power system supplying the shop.

Thanks. Just after I posted and walked away from the computer I thought "I should run a dedicated earth ground and see if that helps"

 

[rgc54]

I have a standard modern 13x40 lathe 2008 model. I converted it to frequency drive completely rewired the machine. Machine has digital readout. I have no trouble with the dro or the frequency drive running together. I did use shielded wire for the vfd on all of the switches.

 

[Engrbill]

Go to DRO Pro's and get the magnetic DRO. Nothing bothers it.

 

[Sniperhandle]

Go to DRO Pro's and get the magnetic DRO. Nothing bothers it.

Yes, Thats where I got the DRO for my 13x40 Kent USA, Great to deal with and I have had no issues with the magnetic scales I got from them, Very nice to be able to cut to fit.

 

[B Nettesheim]

If post # 2 doesn’t work try grounding the machine with its own ground rod. We had to do this on a couple machine shops we wired.

 

[BuffaloBill]

I agree with the grounding being important. Also, if the wiring between VFD and motor is not already shielded, I would do that. There is available, shielded oil resistant stranded 4-conductor cable but it can be quite expensive. Another option is to use metallic flex conduit with wire of your choice.

 

[akajun]

I would say that a magnetic scale Dro is closer to your digital calipers than a glass scale
Tpac tools glass scales dro on three machines
No problems in 6 years
What brand calipers?

 

[Ray123]

I was a machinist long before DROs existed....in time graduated to CNCs. But on my home lathes and Bridgeport I do not use DROs...though about it for years for the Mill, but definitely not needed, accomplished every job with out one for years.

 

[AccelR8]

What brand calipers?

The Mitutoyo caliper is not effected, nor is the Harbor Freight (Pittsburgh) but that caliper is not accurate...OK for comparative measurements within a thou but I wouldn't give them to your inspector!

The caliper that is effected is the no-name "hardened stainless" one in the middle. I was given these in about 2004 by a distributor's rep to try out as they were considering adding them to their line. They've been great except for the EMI issue.

 

[AccelR8]

Thanks everyone for the replies!

 

[AccelR8]

I was a machinist long before DROs existed....in time graduated to CNCs. But on my home lathes and Bridgeport I do not use DROs...though about it for years for the Mill, but definitely not needed, accomplished every job with out one for years.

In my primary education, the shop teacher had us "measure" run out of work in the lathe by holding a piece of chalk against it while it turned. We worked with rulers graduated in 1/32" and various inside and outside dividers.

After school is when I learned about dial indicators, test indicators, micrometers, and then comparitors and so on.

All our machines at work have DROs and I must admit one learns to rely on them. In my home shop, especially in the lathe, I work with direct measurement dials on the cross slide and compound which are really quite accurate. Still, I take direct measurements of the part and cut conservatively to keep "spring" out of it, approaching final dimension with care. But I've been doing AR15 barrels and it would be nice to locate features like gas block shoulder with a DRO instead of a yard stick

 

[Ray123]

In my primary education, the shop teacher had us "measure" run out of work in the lathe by holding a piece of chalk against it while it turned. We worked with rulers graduated in 1/32" and various inside and outside dividers.

After school is when I learned about dial indicators, test indicators, micrometers, and then comparitors and so on.

All our machines at work have DROs and I must admit one learns to rely on them. In my home shop, especially in the lathe, I work with direct measurement dials on the cross slide and compound which are really quite accurate. Still, I take direct measurements of the part and cut conservatively to keep "spring" out of it, approaching final dimension with care. But I've been doing AR15 barrels and it would be nice to locate features like gas block shoulder with a DRO instead of a yard stick

My HS metal shop teacher was only slightly more refined than yours ...but the basics were taught.
When I retired 12 yrs ago there was only one manual lathe Hardinge tool room lathe with a DRO. The one and only manual machine in the whole manufacturing facility. No manual machines were used in production, just CNC over 12 years ago...we were beginning to rely on robotic loaders...my personal Bridgeport came from a large high tech manufacturing facility, the last of the manuals...but no DRO. CNC has no downside except expensive, to own, operate, and maintain, much better than a manual...and fast to program and set up once proficient, and dead on accurate.
But I can't afford one as a hobby machine so...back to the manual, DRO is nice but not necessary to achive high accuracy. I haven't used one for 12 yrs...and don't own a yard stick. But 4 large rollaways and 4 top boxes full of machinist tools, I can usually figure out something.

 

[Dusty Stevens]

My HS metal shop teacher was only slightly more refined than yours ...but the basics were taught.
When I retired 12 yrs ago there was only one manual lathe Hardinge tool room lathe with a DRO. The one and only manual machine in the whole manufacturing facility. No manual machines were used in production, just CNC over 12 years ago...we were beginning to rely on robotic loaders...my personal Bridgeport came from a large high tech manufacturing facility, the last of the manuals...but no DRO. CNC has no downside except expensive, to own, operate, and maintain, much better than a manual...and fast to program and set up once proficient, and dead on accurate.
But I can't afford one as a hobby machine so...back to the manual, DRO is nice but not necessary to achive high accuracy. I haven't used one for 12 yrs...and don't own a yard stick. But 4 large rollaways and 4 top boxes full of machinist tools, I can usually figure out something.

Another few downsides of a decent cnc machine- power requirements, floorspace/headroom, and tooling/operating costs. It costs a bunch of money and time to set up to make a couple pillars or something.

 

[Ray123]

Another few downsides of a decent cnc machine- power requirements, floorspace/headroom, and tooling/operating costs. It costs a bunch of money and time to set up to make a couple pillars or something.

Yep, expensive to own & operate...normally ya have to have a viable product to sell to cover costs...you could knock a hole in the ceiling... but a constant voltage 3 phase ... a phase converter probably won't cut it ...but I never tried. Cause even a mid level CNC is expensive for just a hobby..plus cost of repair and waste disposal, tooling, lubrication..Surprisingly programming, & setup is pretty fast when I was doing it all the time. Simple program a couple of minutes, then set off 2 or 3 tools one minute...draw feature .. looks good run it.. make one or a bunch. CNC is fantastic except for the cost. I ran both. Hogging power and precision I'll take a 30 or 40 HP CNC bedmill, but a 10 hp 10,000 rpm VMX is good for general purposes...Rapids were getting into 2000 IPM and CNC voice communication were new, and changeable between male and female voice. Put a spindle multiplier on run 20,000 rpm through aluminum at almost rapid traverse speed, with precision. Can't do that in a manual machine.
My manual lathes & mill do most everything I need, and it's affordable...but if I were a millionaire or 2... I'd own a CNC

 

[Ksracer]

I converted mine to single phase with a cheap VFD from ebay and it causes no interference with the glass scaled Anilam DRO or the magnetic scaled tailstock readout.
If better grounding like others suggested doesn't fix it, you may look at changing the carrier frequency on the VFD output to see if that helps.