Thread: Milling Machine problem - spindle slow to start

I recently purchased an RF45/MD45/HM46 clone milling machine. After about 10 hours of running the spindle is now slow to spin as though it is binding. It slowly turns and then when it beats friction it spins up to the correct speed. I have swapped tools (it happens with different tools), ripped the drawbar out etc. I cannot find anything binding. Has anyone had this issue or any ideas on what might be the cause?

Are there any belts in the drive or is it all geared? If it was a belt it could be slipping to start with. Is the spindle easy to turn when it is in a mid range gear?

Dead starting cap.*

Stuart

*I guess it could be the centrifugal switch or a couple of other things... but I'd be starting with the cap...... many have failed early on in the life of a new machine.

I would try to isolate the problem

Remove the motor and then turn the spindle by hand in all of the gear speeds , feel for any binding in the gearbox . If all seems OK, then go to the motor and look for faults there . Mike

Not sure what you mean by friction,the only friction that would normally be present would be in the bearings.

I wouldn't be pulling the motor off before checking a few more things.

If its a geared head place it in neutral and see if the motor comes up to speed straight away,if it does rotate the spindle by hand checking if its spins freely.

If its belt drive remove the drive belt from the motor and check if it comes up to speed,then remove the intermediate to spindle belt,see if you can rotate the idler and spindle freely.

The tooling that you are using should have no effect generally on the starting operation of the machine.

Make sure that if there are any spindle brakes that they are releasing

Thanks for the suggestions. The machine is a geared head mill. In neutral it spins up much faster than in gear. In High 3 (fastest speed) it has a 3 sec lag from on to full speed. It even overloaded the power outlet and did not spin at all on one instance. When turning it in for the last 10hrs of use, it would immediately go to full speed without lag.

Originally Posted by variant22

Thanks for the suggestions. The machine is a geared head mill. In neutral it spins up much faster than in gear. In High 3 (fastest speed) it has a 3 sec lag from on to full speed. It even overloaded the power outlet and did not spin at all on one instance. When turning it in for the last 10hrs of use, it would immediately go to full speed without lag.

My DM 45 spins to the full rpm, almost instantly , even when it is in high / 3 . The motor on those models is very easy to remove ( at least on mine it is ) ,you undo the hold down bolts on the flange and it virtually falls off . You can try running the motor while it is of the machine but support it so it wont jump around . Mike

Originally Posted by morrisman

My DM 45 spins to the full rpm, almost instantly , even when it is in high / 3 . The motor on those models is very easy to remove ( at least on mine it is ) ,you undo the hold down bolts on the flange and it virtually falls off . You can try running the motor while it is of the machine but support it so it wont jump around . Mike

Mike are you sure you only have to undo the bolts? I undid the 4 bolts but the motor won't lift off. Almost like it has a retaining clip or something?

I think Stuart's suggestion is worth thinking about. Without the start cap you are relying on the rotating field gradually accelerating the load. With less load (that is, out of gear) it should pick up more quickly.
Before you remove the motor I'd suggest checking the cap out.

Michael

Originally Posted by variant22

Thanks for the suggestions. The machine is a geared head mill. In neutral it spins up much faster than in gear. In High 3 (fastest speed) it has a 3 sec lag from on to full speed. It even overloaded the power outlet and did not spin at all on one instance. When turning it in for the last 10hrs of use, it would immediately go to full speed without lag.

If the spindle does not feel free to turn in neutral, too much preload in the spidle bearings? Or maybe no oil in the bearings / gerbox? Does the quill get hot to touch after maybe 10 minutes of running?
If the spindle feels to turn free in neutral, bad motor (centrifugal switch? or bad capacitor ?)

Originally Posted by variant22

Mike are you sure you only have to undo the bolts? I undid the 4 bolts but the motor won't lift off. Almost like it has a retaining clip or something?

It is probably stuck to the gearbox top , could be the gasket is holding it a tad . Mine has a keyway in the motor shaft that drives the gearbox. Try tapping the side of the motor ..gently with a rubber mallett . You could try gently levering the motor up as well.

But do what the others have suggested re: the starting capacitor in the motor . It may be faulty , its a pretty common fault on the Asian motors Mike

I thought if the start cap was gone, the motor would just sit there and hum until it gets spun in either direction, and then it would come up to speed in that direction.

See if you can rotate the head 180 degree and use the weight of the motor to pop it, put in longer bolts so it can only drop 25mm or so. It took me about 3hours to get my motor off but it had been there for a lot of years.
I did not know these gearboxes had a neutral is it between High and Low i'll have a look for it

Hi Ewan,
It depends on the motor and the cap.
If its a single cap motor and the caps completely dead. it will sit and hum.
But with a two cap motor it will start on the run cap...... though with less torque so slowly.

Strange it poped the breaker though

Stuart

Originally Posted by Stustoys

Hi Ewan,
It depends on the motor and the cap.
If its a single cap motor and the caps completely dead. it will sit and hum.
But with a two cap motor it will start on the run cap...... though with less torque so slowly.

Strange it poped the breaker though

Stuart

Thanks for the notes on the capacitor Stuart. I decided to replace the gearbox oil and whist the head was tilted I was going to check the motor out, but it is proving tough to get off. I may not have responded directly, but the first thing I did (before tilting the head) was popped off the cover and had a look at caps. There are two (branded sok99.com). Interestingly there is one marked 240v, and one marked 415v. I am not sure how to check if they are OK. There was a smell of somewhat toxic plastic when I removed the cover. No idea what it was, but certainly not burnt. I checked out the switch box, and all looked (by eye) OK. Surprisingly the switches were branded as being made by Siemens!

With respect to the caps, what is my next step? Should I just purchase (source?) replacements or is it time to pull out the multimeter?