Bridgeport belt tensioning

[UKRobotics]

I've had to remove my spindle motor and one axis motor whilst retrofitting my machine.

Soon I will have to put them back but the maintaince manual states that I need to tension the belts to a specific rating.

Where can I find a tool for measuring belt tension and what sort of price will I be looking at ?

[UKRobotics]

Can anyone offer any suggestions for this?

Could i just get an old fashioned spring newton meter, hook it round the middle part of the belt and measure how much force it takes to stretch it noticably ?

Is there a better way ?

[machintek]

I asked the same question of Bridgeport and never received a definitive answer. I challenge you to find a value in any book. I especially needed that data for the 10,000 RPM VMC machines.
Thus the answer is to tighten it a prudent amount.

George

[NC Cams]

This is a sliding scale factor that depends on the construction materials used in the belt in concert with whether or not the belt has a tesioner or is relying simply on pulley spacing. If the latter, the amount of thermal growth that you may encounter needs to be considered as a cold running iron housing can tolerate one amount of belt tension but an aluminum housing'd machine that going to be running hot and strong will want another, albeit looser as you have to protect for more tension change from hot to cold.

A number of belt makers specify "droop" measured when you lay a straight edge from pulley to pulley and then push the belt from the tangetly resting straight edge with so much tension applied. The trick is that a nylon stranded belt would deflect differently than say a kevlar belt as opposed to some other tensioning fiber - fiber does make a difference in initial tension as does whether you'r using iron or aluminum pullegs (again because of thermal growth potential).

Having played around with belts a bit in other environments, I'd be inclined to contact the belt supplier for your particular belt - they should be able to provide you with the tension and preferred method for setting same - give them the model and length of belt and tooth count of pulleys and they should be able to give you guidance.

If the belt maker's identification is gone or it's too much hassle to do the research, MACHINETEK's method will have to be more than adequate.

[UKRobotics]

The following text comes from my bridgeport Series 2 interact 4 Maintaince Manual.

Axis Motor/Belt Replacement

Adjust the belt tension so it is tensioned by a force of approximatly 135N (30lbf). If no belt tension meter is available an approximate guide is that at mid position between the pulleys the belt will deflect 6mm (1/4") from its mean position when a force of 70N (16lbf) is exerted on the belt.

Spindle Motor/Belt Replacement

After disconecting or replacing the 'V' belt, reset the tension as follows:
a) With the belt completely slack, mark two lines 500mm apart on the back of the belt. Tighten the belt by jacking out the motor carrier, until the lines are 503.0mm/5.03.5mm apart. Clamp the motor carrier and check that the belt tension is correct.

That may be of use to someone though i'm guessing it is both very machine and belt specific.

That said, the original question still remains, where on earth do i obtain a belt tension meter.?

[camarogod98]

I am doing a retrofit on my interact 4 now to.

I replaced the DC spinlde motor with a AC unit....I adjusted the belt to what i thought was tight enough, then started the spindle and it flapped around at high speed so i just turned the adjuster a little more and it was good. I guess an interact 4 can tap a 1" thread so i will see if it slips....thats the best test i can think of.

Can you please help me with a interact 4 question. Can you send me a picture of one of you tool holders so i can see what kind of retention knob the tool holders use. The retention knob is the thing that screws into the top of the tapered end of the toolholder. The machine grips it there. nobody here in the states can tell me what one it takes. I ordered a "bridgeport" one that fits the 308,412 machines but it is different.

Do you know if you can still get parts for the interact 4's? The hardinge bridgeport company here in the states sucks. they wont even help you. Im in bad need of a maint. manual for my machine and i cannot find one anywhere. I remember you telling me you bought a new one and was wondering if you could give me the info of where i can pick one up at.

good luck with your retro. I almost have mine running....I just cannot figure out what retention knob to buy for it so i cant get a tool in the spindle yet to cut any metal.

[UKRobotics]

I believe it uses standard BT40.

I bought my maintainance manual direct from hardinge bridgeport leicester (uk) for approx $140 dollars.

You can contact them on +44 (0)116 2869900

I'm re-using the existing spindle motor. Just paid about $1600 to get it running. This included a complete clean out, skimming & undercutting of the comm, new motor brushes, new taco brushes, a 5kw autotransformer, a PWM dc motor driver and, single phase conversion for the blower motor and a small variac for the field windings.

Its quite a comlex setup but it would have cost 3 x more to replace it with a new AC motor.

[camarogod98]

Here is a link to what im talking about. It screws into the top of the holder. the machine grips the pull stud.

http://www.jlindustrial.com/catalog/...tosearchpage=Y

there might be a print of a part number for the correct stud in your manauls you could send me. You are going to need to know it anyways when you buy more tooling.