Is It Worth Using Saw Guide Spacers?
POST DATE Aug 17, 2020
Every once in a while, a customer will ask about using spacers to change the target size. The reasoning goes, rather than investing in the right sized saw guide to begin with, you can reduce costs by adding a spacer to your saw guide.
That seems like a quick and easy fix, doesn’t it? And it is quick and easy, which should make you very wary. Because you see, like most quick and easy fixes, this will prove to be a costly decision in the long run.
There are three main areas of concern when it comes to using spacers. They are:
- Tolerance and accuracy
- Proper cleaning
- Maintenance time
Let’s take a look at each individually.
1. Tolerance and accuracy.
Every saw guide has a tolerance, or accuracy. Spacers have their own tolerance, so when you add spacers to the mix, you get what’s called tolerance accumulation. Let’s say your saw guide has a tolerance of /- 0.0005” and your spacer has the exact same tolerance, you now have an accumulated tolerance of /- 0.001”. That might not seem like much, but you’ve just doubled the variation on your cut.
You also need to take into consideration what I call gap control. That’s the gap between the babbitt pad and the saw blade, which is 0.0015”. When you account for your saw guides tolerance, say of /- 0.0005”—which, though standard for many in the industry, isn't the best—there’s no issue there. But you add to that the tolerance for the spacer, which is also /- 0.0005”, and you’re going to have problems.
You’re going to lose gap control. If your gap gets too small, then your babbitt pad begins to act like a disc brake and heats up the saws, which causes downtime. If it’s too big, the within-board deviation will climb and affect the recovery and the quality of your lumber.
Both these issues cost much more than the savings of using spacers.
2. Proper cleaning.
Dirt between saw guides is a problem in every sawmill. It’s time-consuming to do all the necessary cleaning. Adding spacers adds more cleaning: you’re increasing the chances of dirt getting between the saw guides and the spacers.
This amplifies the problem of tolerance accumulation we’ve already covered. This amplification can be very costly in terms of downtime, recovery and quality.
3. Maintenance time.
Finally, adding spacers will increase your maintenance time. We’ve already mentioned that spacers make you lose gap control which will heat up your saws and force you into a change-over. You’re also adding time to properly clean additional equipment.
But on top of all that, you need additional maintenance time on the spacers themselves to make sure that dents and burrs don’t affect your tolerance.
All of this makes your change-overs slower. This means your equipment will be down longer—and we all know what downtime costs per minute. Depending on how many change-overs there are in a month or a year, the cost will be significant.
The final word.
When you think beyond the quick win of finding a shortcut and instead consider the long-term costs, it’s amazing how much of a damaging impact using spacers can have on the operation of your sawmill. If you’re trying to save money, this is not the way. It’s just not worth it.
I’ve visited mills that used two to three spacers per saw guide in order to get the size they want. Based on the three concerns we looked at, I can’t imagine the issues these mills are facing.
In an era where we regularly see mills forced to shut down because they’re not making any money, it’s not just wise to use saw guide spacers. The issues they cause can lead to devastating long-term consequences for the mill. Think twice before you decide to use them.