AL51G belt running off

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dennisa49

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Hello,
My H&F 9 x 20 lathe is spitting the v-belt from the pulley group on the motor driven shaft.
This machine is also sold by Harbour Freight, Grizzly and Jet. There seems to be a runout of .5mm or so on the bottom or A shaft pulley which will be causing the problem.
I would like to know if anyone else has had this problem with this type of machine.
Before I strip the assembly is there something that may have come adrift on the shaft?
Many thanks,
Dennis
 

TonyM

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Hi Dennis. I don't know your particular lathe but the belt should only come off if the pulleys are out of alignment which as you suggest may be caused by something moving. First is to check if they are aligned using a straight edge. Although the pulleys may look as though they are in line with each other, it can be that one pulley is at an angle to the other either in the horizontal plane or vertical plane. You need to check alignment in all planes with straight edges to ensure that first the pulleys are both in the same vertical plane and then in the same horizontal plane. If they are not you will need to adjust accordingly. Runout of the motor shaft is unusual and may indicate bearing problems.
 

RM-MN

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Belts that are loose or worn out can jump out of the pulleys too as can belts that were badly made and have a mismatch or bend somewhere.
 

goldstar31

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ShopShoe raises an interesting comment. ( I hope)
I HAD a 920 but with a Myford spindle. The demerit was that the lowest speed was not 100 rpm but 130rpm in UK voltages. So the UK users soon found a way to reduce the speed by making a new pulley which dropped the speed to a more usable one but used a pair of Round belts.

So having problems, this is perhaps the way to go.

Hope this helps

Norm
 

DJP

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Before any serious repair work, I would check alignment of the pulleys, check for any play in the motor mount and finally try a new belt with the correct V dimension. Belt drives are usually very forgiving in my experience.
 

XD351

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On the 51 g you have the pulley on the motor and another driven by a toothed belt by the motor and to adjust this toothed belt you loosen the motor mounts and lower the motor ,you need to ensure the motor shaft is parallel to the spindle as it will dropp at the rear of the motor when the mount is loosened . You then need to align the face of the motor pulley to the face on the spindle pulley using a straight edge , once those two are aligned do the same for the pulley that is driven by the toothed belt .
Also check the belt tensioner pulley to ensure it is not putting any side load on the belt when you set the tensioner lever .
IMG_0019.JPG
 
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bruedney

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Check the tensioner - Mine was bent/or not in alignment - it caused issues
 

dkwflight

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Hi
I have an enco 9 x 20 lathe. It uses the 5mm 710 and 730mm belts. I think they are too small for the loads.
If the pulleys and tensioner are in line you will not have any trouble with the belts staying on, most of the time.
I find in some grooves/ ratios the belt will be very loose, The 710 is too tight and the 730 is too loose.
I usually use the second slowest speed, sometimes the slowest for bigger shafts, parts.
I am thinking about converting to a VFD motor and timing/toothed belts. I found pulley and belt suppliers on line. I just have to raise the cash and decide on the ratio.
Get a straight edge and make sure your pulleys are in line.
Dennis
 

dennisa49

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Good day and thanks,
I have (I believe) overcome this problem.
The pulley groups are not in perfect alignment. This has not presented as a problem until now. It seems also possible that using the two high speeds applies a fairly high torque loading to the screw that locks the motor shaft pulleys. This allowed the pulley to move outward a little on the shaft.
I have replaced the washer with a machined washer and replaced the 6mm bolt.
I released the head shaft assembly, checked the alignment and retightened the lock nut and locking bolt.
A wipe down of the pulleys with metho and cloth then back to work.
The job I am completing requires a sizeable piece of steel, for this little machine, (30x200), this makes the use of the tensioner far more important.
The pulleys will need to be aligned at some stage, at the moment they are about .5 to .75mm offset. No doubt since new. The belt is running reasonably true. It should not present a major problem.
Thank you all for your input and help,
Kind regards, Dennis
 

dkwflight

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Hi
Something to keep in mind.
I thought the clutch was slipping and finaly found after a while the belt had lost some teeth. The belt was pretty old I think but sometimes things can be missleading.
Good luck
De3nnis
 

Wizard69

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High guys! I see there are 9x20 belt issues being discussed again. I'm of firm belief that the belts on this lathe are undersized and grossly so. The problem as I see it that the power rating of these belts collapses as speed decreases. No I'd be the first to say the the manuals and engineering help on Gates's web site sucks but for the 5M series belts I believe you end up well under a half HP at low RPM's, maybe ls that a quarter horse power depending upon how you read the documents. I don't pretend to be somebody familiar with belt sizing but then again I'm not unfamiliar with the technology. This may very well explain the rather high failure rate people experience on the 9x20 lathes.

By the way I'm not knocking the belt series here. One day I'm hoping to upgrade my 9x20 to support a Micro-V / Poly-V belt solution. If somebody is looking for an upgrade of their lathe this is what I would suggest. Get a belt wide enough (with enough strands) to deliver the HP you need at reduced RPM's.
 

XD351

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They are horrendously expensive compared to say an "A" section belt of the same length and i will never understand why they were specified for this lathe , yes sure they are ok on a sherline or taig as these machines are way smaller than the 9x20 or al50series as we know it in Australia .
 

dennisa49

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Hello, the 5M belts are expensive in Australia ($34.00) from H&F, same from bearing suppliers. A belt upgrade would be good, there is not a lot of room in the cabinet to make the change to new section pulleys.
Is there a higher quality or better material belt available. I keep a spare belt on hand however it would be good not to worry about the life of the belt.
Regards Dennis
 

XD351

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Not that i know of , the main thing is to release the tension off the belt at the end of the day and keep oil away from it . I was going to do an upgrage but ended up selling the machine as i have a bigger lathe as well
 

goldstar31

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Not that i know of , the main thing is to release the tension off the belt at the end of the day and keep oil away from it . I was going to do an upgrade but ended up selling the machine as i have a bigger lathe as well
I agree but I came across the modified pulley that -with the recommended change of belts- gave all the desired useful speeds down to--- 52 rpm. Terrific improvement--- then. It was about 1995 and I moved on.

With no one seemingly interested, I've simply scrapped the pulley.
 

XD351

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Little use to the OP unless you have a link or website they can go to .
I owned the same lathe from early 2k until earlier this year and have never seen or heard of a commercially available conversion otherwise I would have either purchased it or copied it . You can convert it to a wider belt but it would require the manufacture of a complete set of pulleys one of which has a built in clutch and is driven by a timing belt - i never liked that clutch and it cost me a few parting tool tips i can tell you ! The back gear cover would need modifications to allow for longer pulleys also . It sort of gets to the point of diminishing returns for the work needed to modify the machine where the cost outweighs the means and the expense of new belts .
One option is to do a remote pulley set up like i am currently doing to my mini lathe - sort of a bit like what a myford ml10 uses , i am doing this to rid myself of the horrible noisy gears (metal ones i fitted) in the head and as I have already fitted a vfd and 3ph motor previously the cost is minimal . One modification i did do on the al50 (9x20 ) was to fit tumbler gears so it can cut left hand threads , it wasn't pretty but it worked . A similar mod will be done to the mini lathe as the tumbler lever is at the rear of the headstock which is really inconvenient , i'm thinking of a linkage system that connects to a lever mounted on top of the headstock but that is still a little way off !
 

goldstar31

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I have to agree but as I have already repeated where the information could be obtained- literally ad nauseam, i would have expected that a bit of internet searching on the part of the OP would have been attempted. I got the information from the Model Engineer magazine. I actually ran into legal threats in my attempts to put what I considered useful onto the 'net. Understandably, I wisely saw little point in proceeding further.

As for the Myford 10-- blah blah!, I have one but it was built , yet again to a price and there was no tumbler gears etc. There WAS a professional solution but it seems that , like Myford itself, it wasn't economically viable.
Again, the ML10 was modified to assist in screwcutting.

So where have we got to? I suppose there is a need to pay for books and magazines to complement one's hobby rather than what is sometimes a vain attempt otherwise.

Advanced old age seems to dictate getting rid of a lot of hitherto carefully collected information-- and tools/machinery. Well, that's the view of my children who have both Enduring Powers of Attorney on what is left on my frail body and --- my assets. Ouch!

Norm
 

goldstar31

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As an addendum?, I Googled 'Modifications to the 918/920 lathe' and came up with a huge series of comments which quoted what I prattled about-- and the offer of archived information.

What more can be said?

Regards

N

Again, there is yet another web site for Steve Bedair.

I can't think that an old non computer literate old bloke of 88 years is the only one that can get information.
 
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