Hf8x12 Vfd Upgrade The Easy Way

ttt

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Hi,

I have a HF8x12 which I recently upgraded to a VFD drive. I haven't seen any good information on that anywhere so I feel it might be useful to post my experience here.

I got my initial information from this great YouTube video:

Unfortunately the HF8x12 does not have the exact same specs as his lathe.

So, after some research I came up with my own solution, with the goal of keeping it as simple as possible with the smallest amount of changes to the lathe. Only three parts and some electrical cables and terminals are needed:

1. A VFD, in my case a GS2-11P0 from automationdirect ($186 with free shipping) This VFD is 120V and will upconvert to 230V 3-phase. It's 1HP. Documentation included is excellent.

2. A 3-phase motor. The stock motor in the HF8x12 is 3/4HP with a specially long shaft to hold the step pulley, in a metric IEC D71 frame with B3 mounts. I found a motor available in the US which matches these specs pretty closely, i.e. it is a perfect drop in without having to change the motor mount on the lathe. It's a Leeson 192040.00 which is available on Amazon or some other outlets for $200 or less (list price is $356, so look for deals). Specs are 3/4HP, 230V 3-phase, 3600rpm (which is pretty much required for this mod).

3. A bushing for the motor shaft. The stock motor uses a 16mm shaft, while the Leeson motor is 14mm. So I made a 22mm long 2mm thick bronze bushing (ID 14mm, OD 16mm) to be able to use the stock timing pulley of the HF8x12. You need to cut a 5mm keyway into that bushing, I used a hack saw. When I made the bushing I ended up with a bushing which was ID 14.04mm and OD 15.95mm, not quite on target. I simply made up the difference with some 1.5thou and 2thou shim stock to get a tight fit. No one except me will ever see it, right?

You could look out for a new timing pulley instead of using the existing one but they are extremely hard to find with its specs. The stock timing pulley on the HF has a metric 1.5 mod thread pitch (4.71mm) which is NOT compatible with a T5 (5mm pitch) timing pulley commonly available (I tried and wasted $20 on that). It has 19 teeth. You might have some luck finding something like that on some chinese site but I had not such luck. And you would have to broach a 5mm keyway into that anyway which most hobbyist are probably not set up for.


As the shaft of the new motor is much shorter, it's unavoidable that you lose the lower step pulley of the lathe. As an end result and with stock VFD settings that means the upper limit to the rpm of the lathe will be about 1000rpm. Which is plenty for most applications. I overdrive the motor by 25% to 75Hz without any issues so far which pushes the rpm attainable to 1200rpm. I guess you could push that to 90Hz/1500rpm for short runs.

The holes on the B3 mounts of the motor are smaller than the bolts which come with the HF lathe (I believe those are M6 or M8). You will have to enlarge them slightly. In my case I milled slots into them so I have move flexibility moving the motor more into the case than the stock motor was. If the timing belt is pushed out too much and interferes with the V-Belt you might have to make the holes much larger and use washers or mill slots like I did.

To lock in the timing pulley on the the motor shaft you'll need 4 or 5 14mm washers, a larger 5mm washer and an M5 5-10mm screw. I used some large SAE flat washers and drilled 14mm holes using a unibit drill bit. Nothing too critical tolerance wise.

The electrical setup can be daunting if you have never done something like that before. Read the documentation with comes with the VFD. The actual power cables are easy to hook up, i.e. connect T1, T2 and T3 from the VFD to the T1, T2 and T3 poles on the motor and connect 120V to L1 and L2 of the VFD. Don't forget ground.

As for controlling the VFD there are tons of options, consult the documentation. I use the built-in control panel with an extension I built myself.

Lastly to get maximum torque at low rpm set both P20.1 (Slip Compensation) and P20.2 (Auto-torque boost) to 10. Even at 150rpm you'll have really good torque.

Summary of settings I use:

P0.00 230
P0.01 2.4
P0.02 60
P0.03 3600
P0.04 4500 (use this setting at your own risk, it could damage the motor long term)
P1.00 01
P1.01 3
P1.02 3
P2.00 01
P2.01 10
P2.02 10
P8.00 04 (shows % of motor output current)

The rest of the settings are stock.

So far I have to say that this conversion was totally worth it. There is way less vibration and way less motor noise, not to speak of not having the hassle of changing belts all the time.

Videos of my machine:


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IMG_3573.JPG

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Last edited:
ttt, I upgraded my mill to a vfd about a year ago, when I need to mill small parts or drill small holes I overdrive my motor to 120Hz with no issues. From what I have read this will only really reduce torque and can increase wear on the engine bearings but then for high speed you typically are not doing heavy cuts requiring torque and power.

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