# Table feed problem?

• posted

I have an old Enco 135 table feed (Model # 205-6215) on my mill, which has been giving me problems. At low speed it has been very erratic, so I decided to replace the rheostat speed controller. I found a new rheostat, but noticed that there was a 820 ohm resistor across legs 2 and 3 on the old one. The local electronics emporium does not carry 820 ohm resistors and the counter guy said just use a 1K. I am wondering if this advice is correct? I am an electronics lite weight and wonder if I should seek out an 820 ohm or if a 500 or 1000 would be adequate. My problem with the feed is on the low end. I don?t know if the rheostat was just shot or if slightly increasing the resistance would be beneficial or detrimental on the new rheostat. Of course I have no schematic or manual on the drive. Do any of you electronics wizards have any sage advice?

TIA

Jake in Escondido randall (at) fontaine-etal.com

• posted

820 ohms is a standard resistance for 5% tolerance resistors. You didn't say what power it is, but you can find the 1/2 watt resistors at Mouser for 22 cents.

• posted

Can't say how close you need to be on the value without seeing the schematic but you can always add resistors to get the value you need. In series (end to end) resistances just add. Make sure you use the same wattage range as the original. In parallel (side by side) resistance goes by the formula:

1/Rtotal = 1/R1 + 1/R2 ... So, 2 x 1.6Kohm resistors in parallel will give you 800 ohms resistance total - this arrangement (2 of equal value) will double the wattage the resistors are spec'd for as well.

So, given a handful of just about any resistors, by combining them in series/parallel, you can build any value you need. It won't be pretty but it will work... it's just a resistor.

David...

• posted

I solved the resistor problem. I desodered the resistor from the old rheostat, measured the resistance an put it on the new one. (Duh?) I guess I wasn't thinking yesterday.

Well it is all back together, but there is no change in the operation of the table. It is still erratic at low speed. It works great at mid-rang and high. I wish there was some way to change the gearing. I guess I will just have to live with it.

Thanks again for the help.

Jake

FixerDave wrote:

• posted

Hi, Jake,

Another possibility...

I had a very similar erratic-motor problem on my X-axis power feed (made in China). It was also regularly tripping my ground-fault interruptor...which gave me a clue. My unit's problem turned out to be the motor: dirty/oily motor brush holders and a dirty/oily rotor commutator ring. I removed the brushes, partly disassembled the motor by removing the end-plate, and removed the rotor, being very careful not to damage the exposed fine wires on the stator. I cleaned the rotor commutator with a toothbrush and a little denatured alcohol...it needs to dry water and oil free. Then I removed and cleaned the brush holders in the same way...also the carbon brushes. (On my unit the brush holders had to be unsoldered from their wires to allow complete removal.) I let the parts dry thoroughly. After reassembling the motor the power feed ran very smoothly at all speeds, with no more interruptor tripping.

• posted

Thanks Patrick,

My brushes looked pretty good, but I never checked the commutator. I will have to give it a look.

Jake

Patrick Mullarky wrote:

• posted

Hey Patrick, You nailed it. I looked at the commutator and it didn't look too bad, but I cleaned it anyway. The results were very good. The drive works much better. Thanks for the help.

Jake > Thanks Patrick,

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