Thread: Adding VFD to an old drill press - worthwhile? Doable?

Running is easy, the actual conversion may not be so easy.

Whether it's worth it on not is up to you.
A motor will set you back ~$30-50 and the VFD will be ~$140 which is not too bad BUT unless you are comfortable working with Mains AC and then you have to pay a sparky (if you can find on) to install it and maybe a motor rewinder to adapt the motor to run of 240V 3 phase. This may coat you as much as the motor/VFD.
If the DP has poor runout and is generally worn out then it may not be worth it

Just to replace the motor may not be as easy as it sounds
The following is adapted from what I wrote about VFD motor conversions in a previous post

Upgrading can vary from easy to a PITA depending on the machine and the motor.

Firstly you will need to replace the single phase motor with a suitable 3 phase motor but it RARELY stops there

a) Enough space to mount the replacement motor.
Not all motors are the same size and may not physically fit in the space provided.
The easiest arrangement is where the motor is on the outside of the machine so space is not as critical.
If the motor location position has to be moved longer (or shorter) belt(s) may be needed and belt tensioning arrangements allowed for.

b) The motor mounting holes to match
If not, new holes may need to be drilled in the machined motor mounting plate or an adapter plate to be constructed .
Motors that use "feet" are much easier to swap out than motors (such as on bandsaws) that are flange mounted although it's possible to make adapters.

c) The old pulley to match the new motor shaft.
1HP motors tend to use 16/19 mm shafts, 2HP motors tend to use 19/24 mm shafts and 3HP tend to use 24/28 mm shafts.
It's not always possible to bore out the holes in pulleys as it may leave too little material especially if new keyways need to be cut (i.e. not easy)
A simpler alternative is to purchase a new pulley but this may not always be possible e.g. pulley is specialised such as on a DP or BS.

d) The switches on a machine may need to be changed especially if they cannot handle higher currents.

My experiences on converting single to 3phase +VFD machines are
MW lathe: motor changed from 1/2 to 1HP, straight swap but decided to purchase a pulley with a larger bore. Motor cost $50 and VFD was $285, This is a vector controlled VFD so its a cut above the cheapie.

WW lathe: motor changed from 1/2 to 1HP, the bigger motor would not physically fit in space so had to mount it underneath the bench and use a longer belt. a completely new motor mount and tensioning mechanism was needed. This lathe used a special 6 position V-groove pulley and I could not bore out old 16 mm diameter pulley to fit new 19 mm motor shaft - in the end I turned a completely new pulley. Lathe was in very good condition. Motor was $30, VFD was $120 - definitely worth doing

Drill press: motor changed from 1 to 1.5HP, straight swap, motor mount holes in different positions but new motor had a 16mm shaft and had to make a shaft adapter to fit the 19mm bore DP pulley. swats here https://www.woodworkforums.com/f155/vsding-dp-167663 This motor cost me $30 and the VFD $140. The DP was in average condition probably only just worth doing

Compressor: 4HP motor changed to 5HP. Motor mounts were different and new motor shaft was shorter so made an adapter plate to short motor so the pulleys lined up better. 28 mm Pulley was easily swapped. Motor cost $30 and VFD was $225? I bought the compressor for a good price so I was prepared to spend the

Bandsaw; Original 2HP SP flange mount replaced with 3HP 3P foot mount - details here.https://www.woodworkforums.com/f27/19-bs-upgrade-195900
This motor cost me $70 and the VFD was $180. The bandsaw is in very good condition and I deemed it worth doing.

Switch gear was not an issue on any of these as I completely rewired them to run through VFDs.

Thanks Bob! That was exactly what I was looking for, great info.

No, I am not at all comfortable working on mains AC, so it sounds like it's probably not cost effective for me. Not worth getting a sparky in just to avoid changing pulleys!

Originally Posted by rtyuiop

Thanks Bob! That was exactly what I was looking for, great info.

No, I am not at all comfortable working on mains AC, so it sounds like it's probably not cost effective for me. Not worth getting a sparky in just to avoid changing pulleys!

Although it is a main one, there are other useful reasons to install VFDs other than Speed control. e.g. soft start and fast deceleration.

My experience with sparkies and VFDs are

Some have never even heard of them
Some have heard of them but have no interest or experience with them.
Some have heard of them and looked into using them and quickly realise that even for them it's a learning curve that doesn't warrant the time input - why would they be reading VFD manuals and make no money when I can be doing something I already know (e.g. installing powerpoint or wiring up up lights).
Some know how to install specific VFDs that they recommend because they have studied the manuals and feel they can trust them not to muck up.
I haven't met a sparky who will install a VFD that has been purchased unrecommended by a client - I can fully understand that.

I've had this project on my TODO list for a couple of years. And this is the reason why I haven't done it yet:

Originally Posted by BobL

c) The old pulley to match the new motor shaft.
1HP motors tend to use 16/19 mm shafts, 2HP motors tend to use 19/24 mm shafts and 3HP tend to use 24/28 mm shafts.
It's not always possible to bore out the holes in pulleys as it may leave too little material especially if new keyways need to be cut (i.e. not easy)
A simpler alternative is to purchase a new pulley but this may not always be possible e.g. pulley is specialised such as on a DP or BS.

The original motor on my DP has a long thin shaft (14mm I think). The most suitable 3 phase replacement has a short 19mm shaft. Quite apart from the problem Bob highlights about boring out the pulley, I don't think the 3 phase motor's shaft is even long enough to engage in the pulley to any reasonable depth.

Cheers,
Chris

Originally Posted by jack620

I've had this project on my TODO list for a couple of years. And this is the reason why I haven't done it yet:

The original motor on my DP has a long thin shaft (14mm I think). The most suitable 3 phase replacement has a short 19mm shaft. Quite apart from the problem Bob highlights about boring out the pulley, I don't think the 3 phase motor's shaft is even long enough to engage in the pulley to any reasonable depth.

Cheers,
Chris

This is typical of of the problems that arise in these conversions.
A skilled machinist could probably turn up an extension that goes from 14 mmm to 19 mmm but this is not as good as using a motor with the correct length shaft.
A better way would be to get a pulley turned that has a longer hub so that it can be fitted to a shorter shaft but this will be starting to get expensive if you have to get it made.

Keep looking for a motor with a longer shaft - motors from dust extractors sometimes have shafts that are much longer - it's always easier to cut one that is too long than the other way around.

Originally Posted by BobL

Keep looking for a motor with a longer shaft - motors from dust extractors sometimes have shafts that are much longer - it's always easier to cut one that is too long than the other way around.

Will do.