Dyna Mechatronics DM2800

OK, here we go again. You may have seen my last rebuild of a Boxford VMC260 (https://www.mycncuk.com/threads/1597...60-VMC-rebuild). I thought that would be my final one, but while browsing Facebook Marketplace I came across — and accidentally purchased — a Dyna Myte DM2800 (also known as Dyna Mechatronics DM2800).These machines originated from California in the late 80s to early 90s. They are very heavily built, weighing in at just over 316 kg (690 lbs). As you can see in the attached photos, the machine is well constructed and mechanically in pretty much unused condition. However, it has been partly dismantled and it looks like a small bomb went off in the electrical cabinet.

Good Bits:
The machine is in good overall condition and was originally well made, with some nice features such as 16 mm ball screws supported at both ends. It is also fitted with an auto lubrication system and a 10,000 rpm BT30 spindle.
Decent spindle bearings 3 x 7008 angular contact bearings,

Bad Bits: Low-power brushless DC spindle motor (around 900 W), coupled with a tiny spindle drive belt.
The nice Escap disc stepper motors are coupled to the leadscrews with some really tiny belts!
The whole electrical system needs to be replaced.
Information is really scarce!

My plan of action over the next few months is to replace everything in the electrical cabinet, swapping the current DC spindle drive for a more powerful AC servo motor. All the mechanical parts will be stripped and cleaned.

To be continued.

First problem, and I don't even have the main body of the machine home yet!

As I said the stepper motors are really nice disc armature ESCAP motors but they are connected to the 16mm ball screws with some very underwhelming belts,

Attachment 32845

Attachment 32844

It seems that these belts are known for shredding themselves at random times. I thought it would be wise to buy some spares, but these are really obscure belts and not easy to find in the UK.

Attachment 32846

A close alternative but not exact match is the MXL size of belt, but these have a very slightly different pitch of 2.032 vs 2.073, so it may be necessary to replace the pulleys and the belts to try and standardise and make belts easier to source in the future! I can also increase the current belt width to 10mm from the current 8mm to reduce shredding. If anyone know a source for the 40DP belts it would help!

OK a bit of an update, after a lot of looking I eventually found the GT2 or 2GT belts are not only a close match to the originals but also stronger than the originals. This did of course mean replacing all the pulleys, The belt I decided on gave me an almost identical centre distance which is good as the machine has no provision for tensioning the belt!

Belt Spec: GT2-132 66T 10mm width with 50T and 20T pulleys

Both the motor and leadscrew pulleys needed to be modified, the leadscrew pulleys are threaded and screw onto the end of the leadscrew, to allow for pretension of the angular contact bearings that support the leadscrews. The motor pulleys had to be shortened, this was to allow for the wider pulley width. Images below show the new and old pulleys and machining the new pulleys to fit.

Attachment 32862
Attachment 32863
Attachment 32864

With the pulley and belt issued solved I started work on the control electronics, The original control cabinet was a total loss so everything has been replaced, I went for UCCNC UC300ETH 5LPT and the matching UCBB breakout board, this has high speed opto isolated outputs and inputs which has made interfacing a lot simpler. I am also making the move over to the dedicated UCCNC software. Below are some images showing the progress on the control panel, along with the original panel remains!

Attachment 32866
Attachment 32865

Among the nice features of this machine are the stepper motors, these are super low inertia disc stepper motors made by ESCAP as shown below:

Attachment 32867

The link below shows a motion test using the new belt and pulleys, running at 2500mm/min rapid.

https://youtube.com/shorts/m4e0w34zR...TCRlgBoYYA88JS

As you say, looks as if a bomb went off - or a stoned spider wired the original cabinet up! It looks pretty neat now.

Bear in mind that in order to test backlash, you need to approach the same coordinate from both directions. What your test mainly shows is that you aren't losing steps - which is indeed rather helpful.

I tried to use some of those extruded timing pulleys and found that much of my backlash was actually due to movement between the belt and the teeth. I tried different suppliers but suspect they all use similar stock.

https://www.youtube.com/watch?v=aXv_H8yqnt0

In the end I cut my losses and made my own pulleys.

https://www.youtube.com/watch?v=4g2qvoNKiqc

Hi Muzzer,
The video isn't a backlash test, it's just for tuning the top rapid speeds and getting a better idea of the machine's limits. The original machine was capable of 2500 mm/min rapid rates. The motors ideally need to be connected with the windings in parallel, but they have very low inductance and resistance. This caused problems for the drives I'm using, as they basically saw the motor as a short! So they're currently being run in series, which isn't ideal for top speed. However, I've got them running at 2500 mm/min at the moment, and they’ll go up to 2600 before starting to lose steps. Backlash testing (not shown) revealed around 0.008 mm. This is mostly in the leadscrew support bearings, which need a bit more preload.
For future reference you can order timing pulleys in reduced/low-backlash versions, but it’s much more fun to make your own!