V-belt vibration in Ajax AJ8 horizontal milling machine

Hi, this is my first post!

I recently purchased an old Ajax AJ8 horizontal milling machine in remarkably good condition for not a lot of money. I have since fitted a replacement motor and used the machine with good effect but there is a niggle with belt vibration. There is no vertical head, so everything is done on the horizontal spindle.

The machine has two v-belts, one from the motor to a 2-step pulley and the second belt to the main cutter spindle. Both belts are in my opinion correctly tensioned. All bearings are good, lubricated and tooling sharp.

When using a moderate size cutter (e.g. 5" x 1/2" I have noticed some vibration developing in the "slack" side of the final drive belt and this significantly adds to workshop noise. The whole machine is sufficiently heavy that the cut quality appears unaffected. I am mostly milling mild steel, with some cast iron.

I have considered adding an idler pulley to the problem belt, thus shortening the distance between centres as I think this should eliminate the problem. However, before I attempt this fix I would welcome any other suggestions.

On a different but related matter, I need to make a chip tray for the machine and if anyone has the same miller I'd be interested to know what setup you use. I'd like to include a coolant pump and sump.

Brian

Welcome aboard, Brian

You invite other suggestions: Mine would be to convert the machine to Poly-Vee belt drive.

These are much more efficient and effective than the antiquated simple vee belt.

... Millions of Cars and Washing Machines can’t be wrong !!

MichaelG.

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Just found this brief video of one with a modified motor mount.

https://youtu.be/3FbIIZmwxQ8

Useful for reference re. belt lengths

Edited By Michael Gilligan on 31/10/2019 20:45:18

How far can you move the V-belt at the centre of the unsupported length? Is the replacement motor single phase or 3-phase?

Andrew

Brian, just a thought, as it is an older machine and may have sat around for some time before your acquisition, the belts may have taken on a 'set' where they sat round the pulleys and be giving you the vibration. May be worth your while replacing the belts before going further.
DaveD

Currently a 3/4 HP single phase motor but I do have a spare VFD and had originally planned to install a larger 3 phase motor. It's easy to swap the motor as it is now mounted on an adjustable mounting rail. However, the 3/4 HP appears perfectly adequate so far.

The belt moves approximately 10mm under a force of 10N.

The two pulleys measure 70mm / 200mm with a distance between centres of around 430mm.

Thanks for your thoughts - everything is welcome.

There is no significant vibration in the motor drive belt. Incidentally, the motor drive belt is easy to adjust as the motor is on a sliding mount.

The second belt (driving the spindle) runs between two fixed pulleys with no adjustment and that is an additional reason for adding an idler pulley. This belt is long and relatively low speed, whereas the oscillations are relatively high frequency and relate to the cutter being used (6" 18 tooth) and not a "hump" or two in the belt. However, I did try changing the belts with no improvement. I also considered changing to a link belt (as used on my Denford lathe) but doubt it would offer any improvement unless able to absorb the "shock" of the cutting action.

I would have thought that using a 5inch x 1/2 wide cutter is asking a bit too much from a small mill,and is more like likely to be the cause of the noise and vibration than the belts.

That's my video just after adding the motor mount which I have to say has worked very well. However, it doesn't address the problem of upper belt vibration when using larger cutters.

Incidentally, I could post more videos if anyone is interested.

I have just created an album for those not familiar with this machine.

.

I stand by my original suggestion: Poly-Vee belts are lighter and more flexible, as well as being more efficient.

MichaelG.

Edited By Michael Gilligan on 31/10/2019 21:27:48

New poly-v pulleys would cost me significantly more than the machine and that's something I'm trying to avoid. Spending money.

.

They are very easy to make

MichaelG.

[that’s enough from me for now]

But are poly V belts less prone to the OP's reported problem of stretching and snatching than V belts? It seems a lot of heavier duty industrial machinery than an automotive alternator or washing machine is run by V belts. I would not convert it without some thorough research first.

Might just be that cutter is a bit large and coarse for such a small milling machine. It looks rather large for that baby machine. Would be more at home on a Cincinnatti weighing in at five tonnes or so.

Or try buying better quality belts if you bought cheapies last time round.

Edited By Hopper on 01/11/2019 06:43:54

Something wrong here. How do you change to a different spindle speed with that jackshaft? Operating without any form of belt adjustment seems like a bizarre situation. It needs a belt tensioner of some sort, I would suggest. Are you sure the jackshaft is not located through a slot? Is the jackshaft missing a pulley sheave or two?

A simple/cheap solution is to use an automotive cam belt adjuster - often discarded, while still serviceable, at routine cam belt changes.

How fast is the cutter turning? It looks like it is quite speedy, even on minimum speed setting.

MG’s suggestion of a poly-vee belt system is better than simple V belts.

As above, a 1/2” wide, coarse, 5” diameter cutter is likely more than enough for this size of machine.

The intermediate jackshaft is a fixed stub welded to the milling machine base. It appears to be original and offers no form of adjustment for belt tension. The belts are currently set up for best alignment giving a driven speed of approximately 120 RPM. With a 6" cutter that equates to a cutting speed of 57.5 ms-1 which does not seem excessive.

I agree that the coarseness of the cutter is contributing to the vibration, but should point out that when several teeth are engaged with the cut the machine handles the task very well.

.

Hopper

The biggest advantage of Poly-Vee in this situation might be its vastly better ability to wrap around a small diameter pulley.

But, when the focus of the question moved away from technicalities I lost interest.

MichaelG.

[reverting to that’s enough from me mode]

Edit: except to claim the prize for spotting the typo on that belt-settings plate 

Edited By Michael Gilligan on 01/11/2019 09:12:33

On the assumption that the machine didn't vibrate when new the question is why is it doing so now? Poly V-belts may be better, but they're a red herring while the source of the vibration is unknown. A few ideas are:

A 10mm deflection for 10N (1kgf) force seems pretty slack to me, especially on a long unsupported belt. None of my V-belt driven machine tools have a vibration issue, and none of them have idler pulleys.

The second belt looks a bit odd; is the top pulley in line with the intermediate pulley or should the belt be one pulley further out at the top?

While it's unlikely to be the problem a single phase motor is not as smooth as a 3-phase one. It might be that the pulsing characteristic of the single phase motor is exciting something it shouldn't.

Would we be correct in assuming that the vibration only happens when a cut is in progress? If so what is the feedrate? A good starting point for chip load is 4 thou per tooth. When I started using my horizontal mill I used a much smaller chip load, and the whole machine vibrated. My horizontal mill weighs nearty two tons.

What rpm is the cutter running? Looking at the speed chart the lowest value of 150rpm is on the fast side for a 5" cutter in steel.

Andrew

“except to claim the prize for spotting the typo on that belt-settings plate”

And, according to the plate, the top belt should be aligned with the “E” pulley? So someone has moved the top pulley outwards, to achieve the lowest speed possible? Or is the top belt mis-aligned? Plot thickens.

At the traditional cutting speed for average mild steel of 100 feet/min, a 5 inch HSS cutter should run at 80rpm. And a 6 inch cutter should run at 66rpm.

So the machine's lowest speed of 120rpm is way too fast for that oversized cutter if cutting steel

120rpm would suit a 3" cutter.

If you want to use that large cutter on that small machine I think you are going to have to live with the vibration.