Here is a list of all the postings AJAX has made in our forums. Click on a thread name to jump to the thread.
|Thread: diy power on mill|
You might be able to find an old ATX PSU that can supply the required current at 12V. I even picked up a couple of old server PSUs capable of supplying 12V at 80A. They cost me 50p each at a car boot sale. It's quite easy to design a PWM circuit to drive a DC motor like yours - I've done it and it works well.
|Thread: Inverters and stop switches|
Are you sure those crimp connectors have been terminated with the correct amount of force? Did you use a ratchet crimping tool (should work correctly), a pair of pliers, or those cheap crimping pliers with no ratchet action? I wouldn't want to risk any terminations being made incorrectly.
|Thread: V-belt vibration in Ajax AJ8 horizontal milling machine|
OK, probably my last update on this thread and hopefully this is now drawn to a conclusion. I replaced both belts again,but this time with brand new v-belts. Paying attention to earlier advice, I went for slightly increased tension of the top belt by choosing a smaller size. Still no option for fine adjustment of belt tension. I made as trial cut using a small cutter and belt vibration was much diminished. I haven't had a chance to do any more machining but it looks likely to be much better. If I want smoother than this I will have to get round to covering to a vertical head. Many thanks for all your help, Brian.
|Thread: Good practice for lathe circuit design|
Posted by Rainbows on 04/10/2019 13:51:20:
Most NVR switches (or DOL - direct online starters) will not include overload protection. In the event the motor stalls, the motor could overheat before the plug fuse trips. Typically, a higher fuse rating is chosen (e.g. 13A) than the motor rating (e.g. 2A) to accommodate high startup current. Smaller value fuses are likely to blow regularly.
To get around this problem it is common practice to include a manually resettable thermal overload in the supply circuit. This can be set at just above the typical motor run current and will not trip for the short duration of inrush current at startup. The overload protects the motor in the event that it stalls.
To keep things modular you could consider using a short length of DIN rail and DIN connectors. Some VFDs are DIN rail mountable. I use this and it works well.
Noise is a potential problem with motors and VFDs. Check your VFD manual - mine suggests using shielded (e.g. SY cable) between the VFD and motor. It is important to ground the shielding - you can do this by making a pigtail. Control cabling should also be shielded and grounded. My local electrical wholesaler stocks 1.5mm 4 core SY cable (3 phase + earth) for about 70p + VAT per metre.
|Thread: V-belt vibration in Ajax AJ8 horizontal milling machine|
The belts are aligned. I have tried swapping the belts with other spares that I have, but I'm not averse to buying a new belt or two just in case. However, the consensus appears to be to use a smaller / less aggressive cutter to cut down on vibration.
The current pulley configuration gives me the best belt alignment and slowest speed. A slower speed is not possible without a new pulley(s) or changing the motor speed, both of which are likely upgrades.
Dave, thanks so much for your thoughts on this matter. I posted a video which hopefully shows the top belt is currently in alignment. However, it is ONLY aligned with the current (and slowest) pulley selection which happens to suit my needs. The whole setup appears a bit strange as there can only ever be one pair of correctly aligned pulleys, and there is no means to adjust for top belt tension. However, there is no sideways belt deflection.
You are correct in thinking there used to be a motor mounted inside the plinth. Access was very difficult and the motor old, so I replaced it with a newer motor on a sliding rail mounted outside of the plinth. There appears to be a good market on eBay for vintage motors so that gave me some more money back on what I had originally paid. Judging by the number of old screw holes (since filled up) this machine has seen several motors or attempts to get the belt tension just right. At least that problem is sorted and I can use the plinth for storage / adding extra mass / or possibly a coolant system. The rails and motor foot allow me to move the motor in just about any direction, so if the pulleys need changing / flipping that won't be a problem at all.
Correction: I should have said 57.5 metres per minute (not second!) but I think you realised that.
An updated video which may answer some of the issues / questions that have been raised in this thread. Thanks to everyone who has taken the time to read my posts and offer their advice - it is hugely appreciated.
Thanks for posting the photos - it's nice to see other examples of this (and similar) mills to see what others have done. The motor pulley was in poor condition on my machine but that was easily replaced and the others are all in good condition. I think the jury's out on whether it would be worth my while changing to poly-v belts and I should try different cutters / lower spindle speed first.
Out of curiousity, did you have a quick return lever on your machine? Mine was missing the lever and I machined a replacement but haven't really found it necessary. I see you have a t-nut / stop mounted to the front of the table - was this for a power feed add on or simply to limit travel?
The arbour is 3 MT which is handy as it matches my lathe and ER collet set if I decide to use end mills.
I much appreciate your observation about supporting the arbour and how larger horizontal milling machines are used. I never planned to buy a horizontal mill but this one was too good to pass by and I enjoy a new (old) toy to play with. If I ever find time I may try converting it to a vertical mill.
"would any one try using a parting tool a half inch wide !!" -- good point!
Anyone interested in buying a job lot of large milling cutters?
If the current setup allowed a small increase in belt tension I would do so, but as you are now aware there is no means to do so other than changing the belt. Rightly or wrongly, I feel the belt tension is about right apart from the problem of belt vibration/oscillation at higher speed which I'm starting to believe is due to other problems (e.g. feed rate or unsuitability of the cutter).
I doubt changing to a 3 phase motor will fix this problem but I'm happy to convert as I already have a spare VFD. It might also give me some flexibility over spindle speed that I lack through the very limited pulley options.
Regarding the current setup, the pulleys have been chosen to give the slowest spindle speed and best belt alignment.
The vibration only happens when taking a cut using the full width of a 5 or 6" x 1/2" cutter. I have *many* cutters that were included with this mill but most of them are clearly too big for this machine, including slab mills, etc. However, I have enough smaller cutters to know that I can take decent cuts with no vibration. I should point out the 5 and 6" cutters work well (with no vibration) when I can progress the machining on the y axis taking no more than about 2mm at a time.
I will probably be getting rid of the unneeded tooling in due course. A couple of items have already been sold, so the machine has only cost me £60 plus the motor mount purchased new.
The speed chart is something of a red herring as the motor and motor pulley are not original. 120RPM is about the slowest with the current setup and I now understand that may be somewhat high for a larger cutter on this size machine.
Thanks for all your help,
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.
New poly-v pulleys would cost me significantly more than the machine and that's something I'm trying to avoid. Spending money.
I have just created an album for those not familiar with this machine.
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.
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.
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.
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.
Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!
You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.
Click THIS LINK for full contact details.
For subscription issues please see THIS LINK.