[Storen]

Review – Shenhui SH-350 Laser engraving/cutting machine (Chinese E-bay laser cutter 300mm X 500mm)



Shenhui lasers became quite popular recently among hobbyists and enthusiasts because of their low cost (around $1550) and availability on the US market. Unlike many other Chinese brands, Shenhui lasers are stocked in California and shipped fast with domestic couriers. Receiving the machine usually takes about a week and the shipping cost is only a small fraction of what you have to pay for oversee shipment. As far as I know the couriers vary – mine was shipped via Fedex. Another aspect that makes these machines attractive to enthusiasts is that they are relatively easy to support, maintain and modify.


1. Ordering from E-bay and shipping
The ordering process was straight-forward, I received a couple of emails from the seller with shipping information. The seller's English was worse than mine (not a first language for me), there was some confusion with the shipment information. The seller provided wrong phone and address information to the courier and wrong courier company info to me. I would suggest to take these things in your hands and double-check everything with the courier yourself.


2. Packaging
The laser machine came in a rough plywood crate with some basic foam sheets inside. Overall the packaging is good enough and there shouldn't be any damage if the crate is handled the usual way.


3. Housing
The entire housing is made from steel sheet-metal which makes the machine heavy and solid. All the panels had scratches and hit marks. They are manufactured with the loosest tolerances I've seen. All the covers and hinges fill loose and make rattling noises when the machine operates. The locks used for securing the covers in closed position are super cheap and flimsy. The whole machine was quite dirty as well. The top canopy has a transparent window made probably from acrylic. The doors and the removable covers allow for easy access to practically every part of the machine. There is also plenty of space for modifications.


4. Safety
The laser tube is covered with a long lid without a safety switch - If a user opens the lid accidentally while the laser is on he/she will be exposed to the laser radiation, so be extra careful! Because of the poor quality of sheet-metal work on the housing, the radiation from the tube is reflected or exiting directly through several openings. You should always wear protective glasses around this machine. They are not provided in the package, you need to buy them separately. The transparent window on the top doesn't have a protective film or coating therefore it is unsafe to look trough it without protective glasses. The work bed is made from highly reflective steel plate which makes the situation with the reflected radiation even worse.


5. Standard features and accessories

• Laser tube - Cheap Chinese tube that doesn't perform as per specifications. The tube is specified as a 50W but reaches its maximum performance at about 65%. The actual performance is similar to the 35W higher end tubes.

• Drive system - The machine uses very cheap guide rails, belts and steeper motors. I am not an expert but I wouldn't be surprised if these components are among the cheapest on the Asian market. The drive system runs stable and relatively accurate at speeds up to 20mm/s. Any other speed above that mark will produce jaggy curves which became worse at the higher speeds. The maximum speed on the X (long) axis is 500mm/s and 400mm/s on the Y (short) axis. The low precision of the drive system is not going to be a problem when cutting/engraving wood but it will cause issues if you try to cut/engrave fine intricate designs especially at high speeds. When engraving acrylic even at the lowest speeds you will be able to see the fine vertical and horizontal steps. When cutting acrylic you will never have perfect clean “vector” curves. The micro steps are not horrible but are easy to see when you look close. If you try to cut fine details in paper you will have to run the machine at 20mm/s which would also mean burned edges and smoky parts. Overall it works fine and you wont be disappointed as long you don't expect the performance of the top-in-class laser machines.

• Work bed - It provides a manual vertical adjustment for working on deep objects. The size is significantly larger than than the actual operation limits. The bed travels on 4 long vertical screws synchronized and driven by a belt. The screws are securely assembled at the base but very loose at the top which makes the whole tray to shake and vibrate wen the machine is working. This makes the problem with the jaggy cut lines even worse. The tray (bed) itself is made by a sheetmetal frame and removable perforated sheet over it. The top sheet is highly reflective and the perforations are insufficient for proper ventilation which makes the default work bed pretty much unusable in most scenarios. Fortunately the top sheet is attached with screws and is easy to be replaced.

• Ventilation - The machine has a 6” duct at the center of the back panel, below the work bed. It is equipped with a relatively quiet fan that moves some air but to achieve better suction of smoke and fumes it is highly recommended to be upgraded with a bigger blower.

• Light - It comes with a long fluorescent light without a shader on the top so glare could be an issue for some people.

• Rotary attachment - It comes with a basic rotary attachment for engraving cylindrical objects. I haven't tried it yet.

• Laser cooling - The laser is water cooled. The package comes with a small water pump that should be placed inside a container filled with (purified) water and connected with hoses (provided) to the machine. The pump is very quiet when is under water. I can not say anything about the performance as the machine doesn't have temperature indicators.

• Laser head and lens - The head is well made and it comes with a standard 20mm diameter, 2” focal length lens. The lens can be accessed, replaced and cleaned relatively easy. In general it is highly recommended to clean the lens frequently.

• Air assist - The machine comes with a small external air compressor that blows air trough the laser head and moves the smoke from the cutting area. It looks very cheap, runs hot and it is noisy.

• Infrared pointer - Very inaccurate. I tried hard to align it but I was unable to point it exactly over the cutting beam.

• Built-in computer - The machine comes with one of the best Chinese controllers, with a small color LCD display and a basic keyboard on the control panel. The built-in computer allows the machine to read and display files from a USB Flash Drive directly without an external PC.

• USB connection to an external computer - The machine can be controlled very easy with a Windows based computer using free RDWorks software.

• Network connectivity - LAN port allows the machine to be easy connected to an ethernet router and accessed from multiple remote computers. You don't have to use the port on the side of the machine. the cable can be routed under the machine and plugged directly to the controller.

• Software - The RDWorks software is probably the most popular Chinese cutting/engraving control software. It is old and unintuitive but it is quite basic and easy to learn. It supports importing from some really old versions of CorelDraw and AutoCAD via plugins, but could also import directly Adobe Illustrator V.8 files and Inkscape (free software) DXF files.

6. Calibration

• Mirrors - The mirrors on my machine came well aligned so I didn't have to do that myself. The alignment is controlled with simple thumbs screws. There are some instruction in the machine manual as well as some online videos showing how to do this.

• Work bed flatness - The work bed belt can be un-tightened with a single screw, then each of the 4 long vertical screws can be adjusted to achieve a perfectly flat bed. The flatness of the bed is essential for the quality of the cutting/engraving.

• Infrared pointer - Can be adjusted in 2 axis and tighten in position with a single screw.

• Step size - My machine had a serious deviation between the part sizes in the digital files and the cut parts. At the maximum length at the X and Y axis the deviation was around 2mm! This can be corrected very easy in the “vendor settings” inside RDWorks software. To access the vendor parameters you need to type a password: rd8888

• Focal point - The machine comes with a simple rectangular piece of acrylic to measure the distance from the material surface to the laser head. The focal distance from machine to machine will vary a little and it is recommended to check it. There are some online videos showing how to do that.

7. Optional items, upgrades and modifications

• Safety glasses - The laser radiation, direct or reflected, is very dangerous for your eyes! Get a good brand glasses! this is what I got: LS-CD2-OTG CO2/Eximer Laser Safety Glasses Model OTG

• Stand - when the machine operates at high speeds it shakes quite a bit affecting the quality of the results. Initially I tried to use it on a heavy kitchen table but it was vibrating a lot. If you make some custom stand yourself make sure it is massive and rigid. I ended up buying 2 aluminum work platforms on sale for $19 each. They fit the machine size perfectly and are very stable! Here is the exact model: GLA-47WP

• Higher capacity blower - I got iPower 6-inch INLINE DUCT FAN blower 430 CFM. I feel this is the right performance blower for this machine. It provides excellent suction and it is reasonably quiet.

• Ammeter - It is highly recommended to add ta 0-30mA current analog meter to monitor the power going to the laser tube. The settings in the control software provide a universal range for different models and will not match the actual performance of your laser tube. The safe range for these machines is around 5%-65% but is best to measure it with ammeter. If you overpower the tube you will shorten its life or burn it. There is a lot of information about this upgrade online.

• Work bed upgrade - Most laser cutters/engravers come with honey comb tables for less reflection and better ventilation. Similar or better results can be achieved with a custom pin table. There is a lot of info about that online.

• Different focal length lens - The laser head supports standard 20mm 2”FL lenses. I haven't tried it myself but an upgrade should be possible. There are several available options between 1.5” - 4” focal length. The general rule is: shorter focal length will make the laser beam thinner and precise, but also shorter therefore for cutting thicker materials longer focal lengths are used.

• Fume extractor / air filter - If you have to install the machine in a closed area you will need to filter the smoke/fumes. For light use you could use standard 6” duct carbon filter and in-line filter boxes. For heavy use a professional grade fume extractor would be necessary.

• Better compressor - There are a lot of small air-brush compressors. Some of them are very quiet and will have the right performance.

• Closed water container - Most people will simply use a plastic bucket, but any plastic container with a lid/cover would keep the water cleaner. Just drill few holes on the top cover for the hoses and the power cable of the water pump.

• Chiller - If you intend to use the laser at max power or for long work cycles the default cooling may not be sufficient. The 110V CW-3000DF chillers are somewhat standard for these size machines.

• Digital thermometer - A small digital thermometer with a probe can be set to measure the temperature of the water exiting the laser tube. Overheating the laser will shorten its life or burn it.

• USB camera - There are some very inexpensive probe digital cameras with long USB cables. If your computer is close to your laser machine you may attach one to the laser head and to your PC.

• WiFi - I haven't tried that myself but there are a lot of very inexpensive LAN to WiFi adapters that will make the machine accessible over your WiFi network.

• Metal rulers for the work bed - One L-square for the top left corner of the work bed and one vertical for measuring the vertical travel.

• Custom fittings for the work bed vertical adjustment screws - Custom fittings can be cut from acrylic to fit perfectly the top support brackets to eliminate the wobble and vibrations of the work bed.

• Sealing the laser tube compartment - A standard weather seal adhesive tape could be used to seal the laser tube box and contain the radiation better.

[Paul-Anternson]

someone else buy this machine?

[RogerClark]

I bought one of these a few weeks ago, but Im still commissioning it, and have yet to do a cut.

Price was just under $2000 Australian ( around $1400 USD) including shipping interstate ( from a local vendor in Sydney).
They must be buying them in bulk ( by the container load) for $1500 AUD or less to make this economic, as shipping must have cost several hundred dollars because of the size and weight of the unit + packing.

My main problems have been air pockets in the laser tube. I bought a bigger pump to try to get higher flow rate, but the diameter of the pipes make it impossible to increase the flow rate even with using a much more powerful pump.
The bigger pump ended up cavitation and created micro bubbles which made things worse.

So I have gone back to using the pond pump they supplied, but I had to totally release the tube from its, so called, mounting brackets and rotate it, so that the inflow and exit points allowed the bubbles to escape.

But the , so called , mounting brackets are a complete bodge, and its proving to be incredibly difficult to realign the tube onto the first mirror.

The mounting brackets are just a milled aluminium block (about 1 inch high) with a curved cutout for the tube, and the top is a crudely bent piece of galvanised metal strip. 5mm thick pieces of foam rubber are taped around the tube and additional pieces are packed underneath to achieve a rough alignment.

Its cost saving in the extreme, or lack of components in the factory at the time of manufacture, and a bodge to get the machine out of the factory.

Its been impossible for me to realign the laser onto the first mirror, using the existing clamps.

Its possible to get decent clamps from AliExpress for a reasonable price, but they would take weeks to arrive, so it looks like I'm going to have to design and 3D print my own,

Other issues with the machine have been listed by the OP, but additionally...

One of my door catches fell apart and I had to repair it.
One of small bolts which hold the observation window bracket in placed snapped off when tightening, so i just removed it.
The frame assembly that holds the motor to raise and lower the platform ( and the leadscrews), has only been secured by 4 bolts, but there are 12 fixing points, which means that it is not adequately secured in the corners where the lead screws attach. I need to buy more bolts and fix it down correctly.

The main bed is a thin sheet of aluminium, on a not very sturdy metal frame. In the longer term, this will need to be replaced with a thick steel sheet for rigidity.


Laser tube has 45w sustained power on its sticker, but I suspect its only 30 to 35W.


Despite all the negatives, I think its probably value for money, as long as you know you would need to make modifications and upgrades to make it a usable machine.

[KeithOKC]

To the reviewer who posted third thanks for the insights the tube mounting thing is fairly common from what I've seen of less expensive machines but the missing bolts, door falling off, and the thin aluminum bed are all really great points thanks for sharing! Gives people an insight as to why the price varies on these machines. Any other issues? Are they all parts you can fix yourself? Any show stoppers you've run into?

[robertk925]

I have had mine for about 4 months and have been really happy so far. No real problems, and I am getting much better accuracy than Storen seems to be getting. I cut blue tape, silicone, and kapton at 60-100mm/s and curves are smooth and precise. I have etched anodized aluminum and marble at 600dpi and 100mm/s and the graphics are great. I cut up to 1/4" acrylic and the edge looks almost flame polished, with just very faint vertical lines from the laser and air assist pulsing. The laser kerf is approx. .12-.15mm, and I have been holding +-.05mm tolerance on cuts pretty regularly. Here is a thread with some mods that owners have made to their Shenhui lasers.

http://www.cnczone.com/forums/genera...ml#post1773016

[RogerClark]

@KeithOKC

So far I have been able to fix all the faults that I have encountered on the machine.

I'm in the process of 3D printing replacement tube mounting brackets, (as I have an old MendelMax 3D printer).
If I didnt have a 3d printer, I would probably make bracket bases out of wood, as the tube is glass and metal brackets are overkill.

There are also a few more niggles that I intend to fix.

The housing for the laser tube, is made from a sheet of, what appears to be (about) 1mm thick steel. It is pressed into an L section which is secured on the leftband right to some horizontal brackets, i.e it rests on small brackets on the left and right. However the middle of assembly can easily be flexed up and down by at least 1 cm. So I will add a bracket to the back of the machine , in the middle of the back, and fix the laser housing assembly to this to give extra rigidity.

Also, the Stop button was slighly loose, so that when you turn it, to release the button, the whole thing rotates, Not just the button in the middle.
I could not see how to thighten it up, as It looks like a push fit rather than a nut I could tignten up from undermeath, so I have used silicon sealant to glue it into place.

The plasic exhaust duct pipe is about 2m long, so I replaced it with a longer length of flexible aluminium air duct pipe.


I have heard reports that the duct fan is not powerful enough, but mine seems quite strong, so I will reserve judgement on that front.

Anyway.

I hope to fit my my new tube brackets today, so I will report whether this was successful

[robertk925]

A random picture of some cuts on 1/4" thick acrylic to show you the cut quality.

[RogerClark]

@robertk925

What power setting and speed did you use to cut the acrylic?

What max power setting do you have set on the machine its self and what power did you specify in RDWorks ( assuming you are using RDWorks)

Also, just a matter of interest, but the focal distance setting piece of plastic that came with my machine is about 18mm, which is a much bigger distance than Ive seen demonstrated on youtube videos for these machines. So I wonder if I have been sent the wrong "tool"

I guess I will need to do some tests, but at the moment Im still struggling with mirror alignment, as I had to remove and refit the tube because I keep getting air bubbles even though Im using Demineralised water :-(

[Storen]

Yes this is exactly what I was talking about - the edges are rough. The high-end machines make perfect clean cuts. When you cut fine intricate designs intended to be observed from just few inches these steps will kill the perception of finesse.

The machine is quite alright for rough work or for wood because all these issues will be invisible on the blackened (burned) side walls.

[robertk925]

Roger:

I use speed=6 and power=65% to cut 1/4" acrylic. 65% is the max power (20ma) that I like to use on my machine to preserve the laser life, although if I set the % higher it will pump more power (up to 28ma or so I believe).

My lens is a 2" focal length, and I place my material about 5mm away from the nozzle. 18mm seems really far. A few things to check:
1. Is your lens a 2" focal length? I am not sure how to check, perhaps you can measure the height of the curvature and compare to other lenses in a catalog?
2. I am measuring from the tip of the nozzle, but in reality the key dimension is the distance from the workpiece to the lens. You could have a different length nozzle (in your case, 12-13mm shorter) than I do.
3. Is your lens in upside down? Mine was, which I discovered by accident when I went to clean it. As I understand it, the lens should be place flat side towards the table (curved side up).
4. The best way to set your height is to place a piece of acrylic or wood at an angle (approx. at a 10-20 degrees incline to the floor) on your bed then cut a line. Where the cut line (kerf) is the thinnest is your optimum height.
5. I have a few small bubbles at the start but they eventually go away. If you are continually getting bubbles, then your water pump must be sucking in air from somewhere. Make sure your water outlet tube is submerged. I made that mistake, as I wanted to hear the splashing water to make sure the pump was working, but it introduced bubbles into the tank which were then pumped into the tube.

[robertk925]

Wow, you have much higher standards than I do! Like I said, this was some random cutoff part. If I remember correctly the parts that came out of if were pretty good, but I can't remember if I had even dialled in my settings by then or not. I have looked at a lot of other laser cut parts (from Trotec's and Epilog's) and I haven't seen many that were "perfect" unless they were hand finished (wheel or flame polished)

[Storen]

I think all Trotec's and Epilog's models have true servo drive systems. The quality of the cut should be much higher because of that alone. But of course we should compare apples to apples.

[robertk925]

Servos do not have any inherent accuracy advantages over properly designed/tuned steppers systems. Servos are better for high-torque and high speed applications, but steppers can easily handle 200-300mm/s, especially for something with no resistive forces like a laser (as compared to, for example, a CNC machining application).

[gfacer]

More important is the RF lasers the high end systems have and the software....the ability to pulse the RF lasers is probably where the better cuts come from, plus if the software can adjust pulses for corner acceleration

[Storen]

RF Metal Tube is definitely the way to go where high-precision is required. They are also the component that contributes the most to the high price of the top brands. In general RF tubes are installed only on high quality expensive machines. I doubt we will ever see a desktop-class Shenhui with a metal tube

I think the man issues of the glass tubes concerning precision is their low stability and the divergence between the ignition and working power.

The software that comes with Shenhui actually provides some settings for the corner issues. They are somewhat basic tho. For this to work well the software should calculate the optimal settings based on the specifics of the work path. The ones in RDWorks require the user to roughly estimate some values. On some designs they help a lot on others they don't. Its better than not having them I guess.

With that being said I am still more willing to blame the drive system for the issues with Robert's samples.

More important is the RF lasers the high end systems have and the software....the ability to pulse the RF lasers is probably where the better cuts come from, plus if the software can adjust pulses for corner acceleration

[Storen]

Servos do not have any inherent accuracy advantages over properly designed/tuned steppers systems. Servos are better for high-torque and high speed applications, but steppers can easily handle 200-300mm/s, especially for something with no resistive forces like a laser (as compared to, for example, a CNC machining application).

Rob, I only partially agree with your statement. I agree that a well designed stepper system should perform better that poorly designed servo system.

///Servos do not have any inherent accuracy advantages over properly designed/tuned steppers systems///

Actually they do. The Servo motors work in a closed-loop feedback mode with their encoders for error correction and realtime self-adjustment. This is exactly why they are called Servo. Stepper systems cannot take the advantage of that approach because they don't have positional-feedback devises. Therefore they cannot be tuned.

Stepper systems are open-loop, plug-and-play. The digital pulses send by the driver will rotate the motor shaft certain degree (one pole) for each impulse. So the precision relies on the size of the step (the degree). Naturally this “resolution” effect is more pronounced at higher speeds.

Additionally the stepper motor torque degrades very fast with speed increase. That makes them more sensitive to friction related issues at high speeds. They can skip steps and this cannot be corrected because they don't have encoders.

Stepper motors also suffer from vibration and resonance issues (servos don't) and produce considerably more noise and heat.

The stepper motors are cheap and don't require high level of engineering expertise. That's why there are so many Asian brands using them. They vary as prices and quality a lot more than servo systems and people should be more cautious especially when ordering machines from Asia.

There are also the so called “Hybrid” motors. They are different but often they are build around a stepper motor that uses micro-steps dividing the current and using closed-loop feedback. They still work with pulses and not with analog variable current as the true Servo and are inferior as speed and torque performance. Some Asian brands are labeling them as “Hybrid Servo” for marketing reasons

[RogerClark]

@robertk925

Thanks for all the tips.

I will take out the lens and check the focal distance. I recall seeing something on YouTube on how to do this, visually, by projecting an image onto a sheet of paper.

And I will recheck the whole of the optical path alignment, as I'm not that happy with the alignment of the 2nd mirror, as its not very central

However I suspect the problem is likely to be the focal distance.

[robertk925]

I would guess that it is primarily the tube for my "issues". I don't see how the control system can get much better on my machine. I have cut engraved (i.e. using vectors not bitmaps) 2.5mm high text (at 100 and 60mm/s and 10-12% power) and it comes out extremely legibly and perfectly aligned. If the control system were inadequate or inaccurate then it would show up in small vector letters. I have also cut rows of holes as small as .7mm diameter, and they are round and accurate.

If I need precise tolerances I will use my CNC mill (which also runs on steppers by the way!) but I am increasingly using my laser for more and more parts.

[RogerClark]

Well, I still haven't managed to do a single cut yet.

I constantly get bubble appearing after I initially turn the pump on.

I'm using demineralised water and flushed several times.

I even just tried adding a small amount of washing up detergent, but it didn't seem to help.

The air bubbles almost look like they are being created by a vortex where the water enters the tube, but its hard to know for sure.

The only way to get rid of the bubbles is to unclamp the tube and raise the output end, by several inches and rotate the tube. But of course after I refit the tube I have to realign it again as there is a certain amount of adjustment in the clamps.
(Well I ended up having to 3D print some new clamps (to my own design), as the "clamps" that came with the machine was just bits of crudely bent galvanized steel )

But I still have to readjust the first mirror each time :-(

I have searched various forums to see if any had a cure for the bubbles problem, and it seems common, but I could not see a definitive cure.

I did try buying a much larger pump, but because of the length and diameter of the tubes, the pump ended up generating even more bubbles because of cavitation, so I went back to the originally supplied pond pump.

I guess I could buy a load of new plumbing fittings and increase the site of pipe up to a few inches from the tube, as they would almost certainly improve the flow rate, but whether it would help the bubbles problem its hard to know and it would be a lot of effort.

So..
I'm currently at a loss about what to do next :-(

[robertk925]

Roger:

You will always get some bubbles when you first turn on your machine, as some water drains out of the tubes due to gravity when you turn off the pump. However, the bubbles should eventually be forced out, unless:
a. You have an air leak. Is it possible that the connection of your inlet water tube to the laser tube is not completely sealed?
b.Your outlet water tube is not completely submerged in the water tank.
c. Your pump is not completely submerged in the water tank.

I use RV antifreeze, which is pink so it is easier to see how the water is flowing and where the bubbles are located.

To encourage the bubbles to leave your tube you could also just lift up the left side of your machine temporarily (assuming you are physically able or have a friend) instead of moving just the tube. When I first got my laser I was concerned about bubbles as well and did this when I first turned on the machine. However, now I don't worry about it, as the bubbles eventually go away.