Bridgeport power feed

[Clive FosterParticipant @clivefoster55965]

Mark

Glad you have got the electrics thing sorted out.

PM me your e-mail address, can't send stuff via this site, and I'll put a data pack together for you covering the Erskine drive. Do you have a Bridgeport manual? If not I can include my wiring diagram and find an appropriate download link for you.

Easiest way to put the head on is to fix a stout bar pointing vertically up to the table and grab it with a collet in the spindle. Then the table and knee feeds can be used to align the head with the bolt holes. A few extra strategic supports (wood offcuts?) wouldn't hurt. As I recall it I used a 3/4" bar stuck into a 6" (ish) thick lump of timber clamped to the bed when I sorted my head out after buying the machine around 2004/05. I made sure the nose of the quill was set down hard on the wood. After so many years I no longer know if such a thick lump of timber is needed. This time round I shall use a special removing support made by welding a blank end R8 arbor to a 1" steel plate.

Sounds like Zan has done what I briefly considered doing when I got my Bridgeport back in 2004/05 but VFD boxes were way to expensive then. (Especially when a proper, commercial, 440 V output static converter surfaced at £35 and I had a motor in stock to make it a rotary.). I expect his circuit will do you just fine.

This is an example of a commercial VFD set up for a Bridgeport as supplied by Power Capacitors UK (the Transwave folk).

I grabbed it a few months back as the price was right and it was just down the road but I'm unsure if its exactly what I want so I might sell it on. That one is a vector drive unit and the guy who sold it to me said he didn't have any motor heating issues at low speeds despite not having an extra fan to help keep the motor cool. The man who used the Optidrive also made no mention of needing an extra fan.

I'm given to understand that modern Vector Drive inverters are much better at giving the motor exactly the right amount of power at exactly the right time so low speed heating isn't such an issue in machine tool use as it was with the older Voltage/Frequency types.

Considering the single speed toothed belt drive conversion I found a decent belt length and centre distance calculator at Technobots :- **LINK** and ran the American L section belt and pulley data through it.

For the two 40 tooth pulleys and 92 tooth belt the centre to centre distance comes out at 9.75”, 274.65 mm which looks right when waving a tape at my Bridgeport.

Can't quite get that with an 8M20 belt and pulley set. For same speed 1:1 drive nearest is two 36 tooth pulleys and a 105 tooth belt at 276 mm centre to centre distance. Closest I could fined was a 44 – 48 pair giving almost 10% speed reduction at 275.9 mm centres with 115 tooth belt.

I shall probably go for the 115 tooth 8M20 belt and 44 – 48 pulleys as having comfortably more load capacity and running the motor a little faster to help with low speed torque and cooling. Objectively the differences are pretty much academic really.

Clive

Edited By Clive Foster on 27/01/2021 14:20:14

[Oily RagParticipant @oilyrag]

Clive,

I'm interested in what you said in an earlier post about the L section timing belts only being able to transmit slightly less than 2 HP.

Some years back I was involved in manufacturing timing belt conversions for speedway bikes and these used a 2.47:1 reduction ratio on the primary drive. The belt we used was a 1.5" wide and this was perfectly good to handle 65 BHP from a standing start when the clutch was 'dropped' at the starting gate. There is a range of belts which are either polymer, polymer with glass fibre re-enforcing, or a polymer with glass and steel wire re-enforcing. It was the later specification belts we used.

Martin

[Clive FosterParticipant @clivefoster55965]

Martin

Just over 2 hp is what the books say for classic timing belts. Which were designed for light duty work. Metric ones are HDT with different teeth for more power transmission.

OT digression

But there are lots of more sophisticated ones taking much more power. But not always enough. I remember Richard Negus telling me that Gates suggested one of their heavy duty belts would be up to the rear drive job on the Norton Commander rotary. But they got their sums wrong. Stripped the teeth straight off when he wheelied the test bike.

Ooops!

Rotary engine straight line, twist grip connected direct to the speedo needle, power curves can be nice or scary. Your choice.

Had a not so nice little earner changing batteries on speedway and grass track bikes for a while. Did an emergency change for a friends friend once and didn't charge enough so he bought all his mates round.

Clive

[Martyn BallParticipant @martynball23274]

Hi, seriously consider a rotary Convertor.

I bought one and it works perfectly with 1PH/3PH devices. VFD's have to be tuned to the motor power. So, if you have a 2HP motor tuned to a VFD, the coolant pump (@1/4HP) will be overdriven and cause an burn out. With a convertor (of the appropriate rating) it will run all 3PH motors OK. Also, you will need a 5 pin socket (red commando). This will give you 3Ph+ Neutral + Earth. Between any 3PH connections will give 415V, between any phase and neutral will give 230V.In my convertor do not use PH2 for 240V, it's noisy.(it's a suedo phase IE generated by capasitors) Can cause damage to sensitive electronics IE DRO's. Earth everything as normal.

So if you're a hobbiist and not using all machines at the same time, just plug in the appropriate machine and go. The only down point I would say is you running another motor, but you can turn it off when not required. Runs off a standard 13AMP supply, but recommend a 16AMP supply if your machine has high start current surge. Martyn

PS these convertors aren't small.

[Barry Smith 4Participant @barrysmith4]

Hi, I went down a similar route with both of the manual bridgeports I have owned. They both had belt drive heads which is simpler in some ways but to get to use a 220v vfd you may have to change out the motor. I always upgrade the vfd to 1 HP over the rating of the motor and have had no problems with lack of torque. The only time I had this issue was when using a diy capacitor based converter. Now VFDs are so cheap I would not even go down that route.

I tend to use filters and contractors on the mains side of the vfd but otherwise use the digital controller of the vfd to do start, stop estop, fwd/rev and the contactor for isolation. You may find that you need to change out the electronic fuse on your mains supply to avoid tripping. Never had any problems with noise on the house electrical system.

I used the transformer which came with the original electrics to power the Erskine box (until it stopped working), light and an Align power feed on the table z. I use a separate 240v suds. I did think of going over to a dc motor on the series 1 CNC I have which has the variable belt drive fitted as I have some dc control boards. DC motors can give you a lot more overload torque than ac 3 phase but this conversion seems less common, perhaps its the dc motors use in small wind generators? If your using the original BP table feed its worth your while checking and if needed replacing the wires in the control box/motor. To replace the Erskine, I used a kbb anti plugging dc drive off ebay which works fine and has the benefits of being more modern components wise and smaller.

This week I am going to try the Chinese 220V single to 440V three phase route keeping the speed preselectors on the main spindle 2 speed motors and then digital controls for for/rev, stop/start, estop and speed (it's not a bridgeport). At £80 I could not resist. I will keep you posted.

Barry

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