Husqvarna Homeqwner Saw Plastic Construction

[Chris-PA]

I've been trying to figure out why Husky uses the construction they do. All the low end plastic Huskys use a "semi-clamshell" design, where the lower metal cap is an insert molded into the plastic chassis. This seems to be an evolution from the Partner 400 design were there was no metal for the bottom end, which Husky also used. Later on they added the metal insert.

Poulan meanwhile made their clamshells as a self contained unit with a metal cap on the bottom. Once the sealant sets you can remove the engine from the chassis without taking it apart. You can build it up separately, swap it into other chassis, etc. My Husky 142 was made this way, and then they went back to the attached lower cap, but Poulan never has.

I can't really think of a single advantage to the construction Husky uses - it can't be weight as they still have a metal insert and the cap weighs nothing anyway. Does anyone know why they do this?

 

[thomas1]

For being a Principal Hardware Engineer, who knows international business and is smarter than everyone else, you sure are befuddled by lots of stuff.

 

[w8ye]

There have been a lot of model airplane engines cobbled up from those all metal clamshell designed chainsaw engines from Echo, Poulan, Homelite, and Stihl. Don't remember any Husqvarna's - probably for the reason you mentioned with the plastic lower bearing cap?

I have a Husqvarna 350 which works well and a later model Stihl 025. They are nice homeowner style chainsaws and the plastic has never been a problem.

 

[Chris-PA]

For being a Principal Hardware Engineer, who knows international business and is smarter than everyone else, you sure are befuddled by lots of stuff.

People who think about things tend to get confused, but it is a temporary state.

People who don't think about things are confused too, but it is permanent, and accumulates.

It is unfortunate that so many reach adulthood without learning basic skills such as how to think, and then they get angry and resentful. Instead of making the effort to use their brains, they take their frustrations out on others who do. I also find that many who were not taught to think also lack basic socialization skills, such as manners.

 

[SawTroll]

There have been a lot of model airplane engines cobbled up from those all metal clamshell designed chainsaw engines from Echo, Poulan, Homelite, and Stihl. Don't remember any Husqvarna's - probably for the reason you mentioned with the plastic lower bearing cap?

I have a Husqvarna 350 which works well and a later model Stihl 025. They are nice homeowner style chainsaws and the plastic has never been a problem.

The Husky 350 isn't really a clamshell, as the upper part of the case isn't integrated with the cylinder....:msp_wink:

 

[Modifiedmark]

I'm not so sure that Partner started that horizontal design.I have to think it might have first come out on the crappy Jonsered 500 series. I'm pretty sure it was a Electrolux deal any way you look at it.

 

[Chris-PA]

OK, but setting aside how it got started, why do they do it now? Why not leave the bottom cap as a separate piece rather than mold it into the housing?

 

[stihl023/5]

I don't think that plastic bottom is much of an issue there are a lot of those home owner saws out there taking a beating.

 

[Chris-PA]

I don't think that plastic bottom is much of an issue there are a lot of those home owner saws out there taking a beating.

Yeah, it seems to work - but they aren't plastic bottoms any more. They are metal, but the metal pan is attached to the chassis. That means you can't build the engine up separately and just bolt it in. All the same parts and engine design, just harder to work with - for what purpose?

 

[Chris-PA]

Basically, why mold it in like this?:

 

[SawTroll]

Yeah, it seems to work - but they aren't plastic bottoms any more. They are metal, but the metal pan is attached to the chassis. That means you can't build the engine up separately and just bolt it in. All the same parts and engine design, just harder to work with - for what purpose?

What's the point with that - I believe even Stihl have stopped using a seperate cap under the transfer on their newer "clamshell" models.....

 

[Chris-PA]

Well, that was the question! You have all the same pieces, the engine design is the same. On the 240 the upper cylinder is clearly a minor variation of a Poulan Pro engine, which is built with the separate cap.

Maybe just a minor production flow issue.

 

[Philbert]

This was new to me. I am familiar with the STIHL MS 250 type saws where the complete motor can be removed intact from the plastic case. Always amazed at how many design variations there are on chainsaws, especially when I start to think that I know something about them.

Just trying to guess what might make a design engineer do this (total speculation):

- Money. Maybe molding in the part saves a few cents per saw in assembly time?

- Money. Maybe molding in the part saves the cost of 4 bolts/screws?

- Stability. Maybe this 'integrates' the motor more firmly to the plastic housing, reducing vibration or movement, or allows them to simplify other parts of the plastic housing?

- Embarrassment. Maybe the engineer once placed a motor base into the plastic housing too early and it stuck. Then, to avoid admitting his mistake, justified this by saying, "Of course I did this in order to . . . (blah, blah, blah)", costing Husqvarna millions of dollars in tooling costs instead of hurting his pride?

Philbert

 

[stihl023/5]

- Embarrassment. Maybe the engineer once placed a motor base into the plastic housing too early and it stuck. Then, to avoid admitting his mistake, justified this by saying, "Of course I did this in order to . . . (blah, blah, blah)", costing Husqvarna millions of dollars in tooling costs instead of hurting his pride?

Philbert

That sounds logical!

 

[Chris-PA]

This was new to me. I am familiar with the STIHL MS 250 type saws where the complete motor can be removed intact from the plastic case. Always amazed at how many design variations there are on chainsaws, especially when I start to think that I know something about them.

Just trying to guess what might make a design engineer do this (total speculation):

- Money. Maybe molding in the part saves a few cents per saw in assembly time?

- Money. Maybe molding in the part saves the cost of 4 bolts/screws?

- Stability. Maybe this 'integrates' the motor more firmly to the plastic housing, reducing vibration or movement, or allows them to simplify other parts of the plastic housing?

- Embarrassment. Maybe the engineer once placed a motor base into the plastic housing too early and it stuck. Then, to avoid admitting his mistake, justified this by saying, "Of course I did this in order to . . . (blah, blah, blah)", costing Husqvarna millions of dollars in tooling costs instead of hurting his pride?

Philbert

I'm tempted to say they're just used to thinking about building the engine in the case like with a "pro" saw, but I doubt it is that arbitrary. Manufacturing engineers spend a lot of time mapping out work flow and looking at process times, etc.

My assumption was that it would make more sense in production to build the engines separately - different kinds of work and skills, sealant dispensers, etc. But maybe not. To build this type of engine where the 4 bolts that hold it together also hold it in, with a separate cap you'd have to clamp it together and let the sealant set up, and then you could put it in the chassis. This way you can do it all on one step and once the bolts are torqued it is done. I'll bet that is it.

 

[thomas1]

Well, that was the question! You have all the same pieces, the engine design is the same. On the 240 the upper cylinder is clearly a minor variation of a Poulan Pro engine, which is built with the separate cap.

Maybe just a minor production flow issue.

You don't have all the same parts. The fasteners that hold the engine to the chassis are eliminated. As is the step of bolting the engine in the chassis.

 

[Philbert]

(now that I have had 15 minutes or so to think about this . . .)

If you look at early saws, they had engines with gas and oil tanks bolted on, mounted onto some type of frame, etc. Modern saws are more 'integrated', with fuel and oil tanks cast/molded into the housings, handles integrated, threaded mounts cast in, etc., etc. This could be an experiment moving more in that direction. For a lower end, consumer type product, replacing parts and serviceability is less of a factor than reducing costs/price points.

Maybe this is a step closer to the Husqvarna 3D printer chainsaws that you will order via a download and 'print' at home?

3D-printed gun blueprints pulled from Internet, at request of State Department - CBS News


Philbert

 

[machinisttx]

OK, but setting aside how it got started, why do they do it now? Why not leave the bottom cap as a separate piece rather than mold it into the housing?

My guess, from a machinist's point of view, is that it eliminates the molding and machining processes of another part as well as simplifying the assembly a bit.

 

[Chris-PA]

You don't have all the same parts. The fasteners that hold the engine to the chassis are eliminated. As is the step of bolting the engine in the chassis.

No, there are 4 bolts holding the engine to the chassis, exactly as in my 42cc Poulans. The bolts come up from the bottom, through the cap and into the upper cylinder. The only difference is that here the cap is attached to the plastic case, while with the Poulans it is a separate piece.

The 142 and my Poulan 2775 have 4 bolts that hold the cap on, and 4 more that hold the engine in - this is nicer to work on but requires more fasteners.

 

[Chris-PA]

My guess, from a machinist's point of view, is that it eliminates the molding and machining processes of another part as well as simplifying the assembly a bit.

No parts are eliminated. The metal cap must be cast first, and then it becomes an insert when the case is molded.