Threading feed table & calculators, do not match.

I know i sussed this out previously so that i only needed to change one pair of gears to cut most standard threads. But its all lost

Tried the online calculators and they do not match my machine, the gears given in my manual do not actually fit the machine...

SPG2109 lathe, similar to the DBVS7 and 210 lathes from various sellers, except mine had a 2 speed gearbox and the motor drives the spindle direct with a belt. The manual shows 2 belts with an idler pulley.

Its a metric leadscrew 2mm. 40 tooth drive from the spindle, i can have upto 3 pairs of gears, the 3rd set being on the leadscrew itself.

For a 1mm thread the manual shows Spindle (40) to a 60T on the 1st shaft, a 52T on the 2nd shaft and an 80 on the leadscrew.

Except that does not fit, that choice needs a shaft a few mm longer than it is. But i tested it with a 66 , 40 and 80 and also 84, 24, and 80, both of these produce a 1mm thread. This does not match the calculators though.

Please help me get my sanity back, i know it wa s apain in the whatsit previously but i cracked it and that data is probably tucked away safe or its on a hard drive that failed or got removed

Thanks.

Is there a spacer stuck in one of the gears you took off?

Are you pivoting the banjo when the gears have been fitted to bring the 60T into mesh with the 40T on the spindle?

Yep pivoting the banjo, but the banjo is not long enough to get the gearset in the manual. Its not a spacer issue.

The leadscrew gear has a dedicated spacer, but the other 2 just use smaller gears for spacers.

Dave,

The 60T and the 52T are only idler gears. They can be any size that fits to allow engagement from the spindle 40T and the leadscrew 80T gear.

The drive ratio is 1:2 which clearly means the 2mm pitch leadscrew turns at half speed to the spindle, giving a 1mm pitch thread on the workpiece.

There are usually hundreds of theoretical gear combinations that will give the same pspindle to leadscrew ratio, but only a few (if any!) will physically fit normally.

Andrew

Yeah, i do remember creating a list of the correct gears to use, but it seems to have vanished and the gear calcs do not seem to list the correct ratio's.

I do remember that the first gear shaft when used wuth a single gear, just reverses the direction of the drive to get the leadscrew going the correct way. The 2nd shaft is where 99% of it happens. Most ratios can be achieved on that shaft alone with a few others on the first or leadscrew shafts.

My issue is which calculator did i use to create the working gear sets? Or what was the formula? Seen several but they dont allow upto 3 pairs to be used. A couple wouldnt let me change the leadscrew pitch.

Thanks.

I have the AMD210 from amadeal which I think is the same as yours, I had problems with fitting recommended gears as banjo slot was not long enough, so made the slot longer on the mill, Bobs your uncle , problem solved.

Slot only needed extending by a few mm.

Replaced the banjo locking screw with a shaft that extends through o hole in the cover and can engage or disengage the banjo at will, much quieter when running if you do not need auto feed, plus added a handwheel on the end of the feedscrew.

 

I think i need to make a longer banjo, possibly with 2 slots instead of the one?

No issues with the gears meshing with the spindle gear, you could make the banjo a few inches longer withoug issues.

I did grind the banjo nuts slightly, they slot is rounded at the ends and the nuts were square.

Have you got the 2 speed gearbox and does the motor drive the spindle directly with a belt? The manual that came with it showed the motore with a belt to an idler pulley and then onto the drive spindle.

Yes! 2 speed gearbox and motor drive same, the manual you get refers to an earlier model.I have been very pleased with mine.it does what I need it to do.

After 4 years the bearings started to rumble, changed them with Timken bearings and its running well again.

One thing to watch if you need to do the same, my manual shows 2 bearings the same, but they are in fact different.

Shows 2 x 30206 taper bearings, but the one closest to the chuck on mine is actually a 32007. A slightly beefier part.

If yours a Metric 2mm leadscrew? How do you work out your screwcutting gears?

Hello Dave Smith the 16th,

If one goes back to first principles, then the following equation applies

Required pitch = conversion [metric to imperial] x ratio in change wheels x lead screw pitch. Taking your question for cutting 8 tpi at the start of this thread and putting values into the equation, using a conversion of 127/120, we get the following

25.4/8 = 127/120 x R x 2 which gives 3.175 = 127/120 x R x 2.

Working through---- R = 3.175 x 120 divided by [127 x 2] giving R = 1.5. So with a driver wheel of 60T, the driven wheel on the lead screw will be 40T

For another value of say 10 tpi, the sum is 2.54 = 127/120 x R' x 2 and R' becomes 1.2 so your driver wheel then becomes 48 T for a lead screw wheel of 40 T . I'll leave you to work out a table to suit your needs

Regards Brian

Edit  I forgot to add. The conversion wheels are in awkward sizes and can be replaced with wheels in the simpler ratio of 18/17, or multiples thereof such as 36/34. I hope that help you

Edited By Brian Wood on 19/06/2016 18:46:25

Thanks, your right about the awkward sizes, i dont seem to have any that i need

60 - 40 i can do. No 48 tooth gear though.

For a 10tpi thread my manual shows spindle 40T to 60T on shaft 1, the 60T drives a 40T with a 66T on the same shaft, the 66T drives a 52T leadscrew.

Annoyingly i had it all sorted (Metric anyway) but i have lost the paperwork or files with the correct data and formula that worked with my machine. The gear calculators do not seem to cater for me having 2 pairs of changegears with the spindle gear and leadscrew separate.

Leadscrew 2mm pitch 100%, so its not that.

Thanks.

I was showing you how to work out a table for yourself, not trying to solve your particular situation and I've given you a formula that will do it for any pitch the machine can cope with.

On your second point, the ratio 48/40 can be geared equally well as 60/50 instead as I have no idea what gears you have or how you can arrange them on your lathe. A copy of the table in your manual would help as I can't follow things as you describe them.

Brian

It might be worth you knocking up a spread sheet to work out what pitches the lathe actually cuts particularly imperial on a metric lathe and the same but the other way round.

I'd guess that you know that idlers just reverse rotation and you can use as many as you like where ever you like. 1mm on a 2mm pitch lead screw with 40T on the spindle just needs 80T on the lead screw. You can fit what ever you like in between just use sufficient to get the correct hand thread. Not being able to find a suitable arrangement is highly unlikely otherwise they wouldn't suggest that you can cut a 1mm pitch thread. They might not supply a nice drawing showing the gearing arrangement.

John

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Sorry guys, i got distracted with other projects but now need to rattle my brain on this one.

I have a chart of what gears to use but its useless, the ones in orange will not physically fit onto the bar or in the space between the leadscrew gear and the top of the bar the gears attach to.

There are probably more that do not work, but not had a chance to try them yet. I think the 1.75 comes out wrong also?

What am I missing? Someone please knock some sense into me Thanks.

A 60tooth gear in the A position only just reaches the spindle gear, i had to grind a small chamfer in the locking nuts. Anything less will not reach the 40tooth spindle gear. 

Manual must be for an old model where they changed the design and possibly even the leadscrew pitch?

Thanks

Edited By Dave Smith the 16th on 09/07/2016 02:32:54

Hi Dave,

If I understand your threading table problems correctly the orange coloured don't fit. The metric part with 0.7mm pitch; the 40T gear on the spindle is driving the 50T (A)gear which is keyed to a 35T (B) gear which is driving a 72T idler gear that is driving the 80T gear on leadscrew. Since the 72T gear is an idler gear you can use a larger gear or a smaller gear so the gear train will fit your banjo.

You can find a change gear calculator here. I hope this can help you on your way.

Thor

Are you also swinging the arm that carries the gear train ?

Just wondering if you are only adjusting the position of the gears in the slot. Usually the arm, often called a banjo can be pivoted around the lead screw axis. So in use the gear train will usually be set up on the banjo and then the banjo swung to mesh gear A with the gear on the spindle.

What does the letter H signify ??

Just add in 1mm pitch you can use any gear you like instead of the 52. It's just an idler.

Also I assume that the H indicates a spacer.

While I'm at it you seem to have a 2mm pitch lead screw. When there is no compound gear in the train the 40T on the spindle is effectively driving the gear on the lead screw and any gears can be used in between.

There are also cases where an idler is used to drive a compound gear pair so again any size of gear could be used.

John

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Edited By Ajohnw on 09/07/2016 10:05:16

Edited By Ajohnw on 09/07/2016 10:06:43

Edited By Ajohnw on 09/07/2016 10:14:32

Maybe you can provide a photo or two. As you were told in an earlier post the 60 and 52 are just idlers so can be any size. Use bigger ones if you need to.

Maybe this will help. I've highlighted all of the idlers in green.

If I've made a mistake I'm sure some one will mention it - I hope

The way to think about idlers is to consider a train of 3 gears each one meshed with the next one. The gear at the top rotates say one tooth, the middle tooth rotates 1 tooth too and so does the one at the end. So the gear ratio is determined by the tooth count of the top and bottom gears. There can be any number of teeth on the one in the middle.

The only other factor needed is the number of teeth on the spindle gear which is driving the train. I single gear meshed with that is an idler.

John

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Edited By Ajohnw on 09/07/2016 10:47:53

Photos of your set up are pretty much essential for anyone to see what the problem may be at this stage.